Encoder, decoder, encoding method, and decoding method

ABSTRACT

An encoder includes: circuitry; and memory, in which using the memory, the circuitry, in affine motion compensation prediction in inter prediction for a current block, places a limit on a range within which motion estimation or motion compensation is performed, and performs the motion compensation for the current block.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a U.S. continuation application of PCT InternationalPatent Application Number PCT/JP2018/039740 filed on Oct. 25, 2018,claiming the benefit of priority of U.S. Provisional Patent ApplicationNo. 62/577,955 filed on Oct. 27, 2017, the entire contents of which arehereby incorporated by reference.

BACKGROUND 1. Technical Field

The present disclosure relates to an encoder, a decoder, an encodingmethod, and a decoding method.

2. Description of the Related Art

There has been H.265 as the video coding standard. H.265 is alsoreferred to as High-Efficiency Video Coding (HEVC).

SUMMARY

An encoder according to an aspect of the present disclosure includescircuitry and memory. Using the memory, the circuitry, in affine motioncompensation prediction in inter prediction for a current block, placesa limit on a range within which motion estimation or motion compensationis performed, and performs the motion compensation for the currentblock.

Note that these general and specific aspects may be implemented using asystem, a device, a method, an integrated circuit, a computer program, acomputer readable recording medium such as a CD-ROM, or any combinationof systems, devices, methods, integrated circuits, computer programs orrecording media.

BRIEF DESCRIPTION OF DRAWINGS

These and other objects, advantages and features of the disclosure willbecome apparent from the following description thereof taken inconjunction with the accompanying drawings that illustrate a specificembodiment of the present disclosure.

FIG. 1 is a block diagram illustrating a functional configuration of anencoder according to Embodiment 1;

FIG. 2 illustrates one example of block splitting according toEmbodiment 1;

FIG. 3 is a chart indicating transform basis functions for eachtransform type;

FIG. 4A illustrates one example of a filter shape used in ALF;

FIG. 4B illustrates another example of a filter shape used in ALF;

FIG. 4C illustrates another example of a filter shape used in ALF;

FIG. 5A illustrates 67 intra prediction modes used in intra prediction;

FIG. 5B is a flow chart for illustrating an outline of a predictionimage correction process performed via OBMC processing;

FIG. 5C is a conceptual diagram for illustrating an outline of aprediction image correction process performed via OBMC processing;

FIG. 5D illustrates one example of FRUC;

FIG. 6 is for illustrating pattern matching (bilateral matching) betweentwo blocks along a motion trajectory;

FIG. 7 is for illustrating pattern matching (template matching) betweena template in the current picture and a block in a reference picture;

FIG. 8 is for illustrating a model assuming uniform linear motion;

FIG. 9A is for illustrating deriving a motion vector of each sub-blockbased on motion vectors of neighboring blocks;

FIG. 9B is for illustrating an outline of a process for deriving amotion vector via merge mode;

FIG. 9C is a conceptual diagram for illustrating an outline of DMVRprocessing;

FIG. 9D is for illustrating an outline of a prediction image generationmethod using a luminance correction process performed via LICprocessing;

FIG. 10 is a block diagram illustrating a functional configuration of adecoder according to Embodiment 1;

FIG. 11 is a conceptual diagram for illustrating affine inter mode ofaffine motion compensation prediction;

FIG. 12A is a conceptual diagram for illustrating affine merge mode ofaffine motion compensation prediction;

FIG. 12B is a conceptual diagram for illustrating affine merge mode ofaffine motion compensation prediction;

FIG. 13 is a block diagram illustrating an internal configuration foraffine motion compensation prediction in the inter predictor included inthe encoder according to Embodiment 1;

FIG. 14 is a flow chart for illustrating the first processing procedurefor affine inter mode of affine motion compensation performed by theinter predictor in the encoder according to Embodiment 1;

FIG. 15 is a flow chart for illustrating the second processing procedurefor affine inter mode of affine motion compensation performed by theinter predictor in the encoder according to Embodiment 1;

FIG. 16 is a flow chart for illustrating the first processing procedurefor affine merge mode of affine motion compensation performed by theinter predictor in the encoder according to Embodiment 1;

FIG. 17 is a flow chart for illustrating the second processing procedurefor affine merge mode of affine motion compensation performed by theinter predictor in the encoder according to Embodiment 1;

FIG. 18 is a block diagram illustrating an implementation example of theencoder according to Embodiment 1;

FIG. 19 is a flow chart for illustrating an operation example of theencoder according to Embodiment 1;

FIG. 20 is a block diagram illustrating an implementation example of thedecoder according to Embodiment 1;

FIG. 21 is a flow chart for illustrating an operation example of thedecoder according to Embodiment 1;

FIG. 22 illustrates an overall configuration of a content providingsystem for implementing a content distribution service;

FIG. 23 illustrates one example of an encoding structure in scalableencoding;

FIG. 24 illustrates one example of an encoding structure in scalableencoding;

FIG. 25 illustrates an example of a display screen of a web page;

FIG. 26 illustrates an example of a display screen of a web page;

FIG. 27 illustrates one example of a smartphone; and

FIG. 28 is a block diagram illustrating a configuration example of asmartphone.

DETAILED DESCRIPTION OF THE EMBODIMENTS

For example, an encoder according to an aspect of the present disclosureincludes circuitry and memory. Using the memory, the circuitry, inaffine motion compensation prediction in inter prediction for a currentblock, places a limit on a range within which motion estimation ormotion compensation is performed, and performs the motion compensationfor the current block.

With this, the encoder can efficiently perform motion compensation usingaffine motion compensation. More specifically, a limit is placed on arange within which motion estimation or motion compensation is performedin affine motion compensation prediction, thereby allowing reduction inthe variation between control point motion vectors in affine motioncompensation prediction. Accordingly, the affine motion compensationprediction is more likely to be selected in the inter perdition, andthus the motion compensation can be efficiently performed using affinemotion compensation. It is also possible to place a limit on the regionof a reference picture to be obtained, thereby having the possibility ofreducing the memory bandwidth required for an external memory i.e. aframe memory.

Here, for example, in the affine motion compensation prediction, thelimit on the range within which the motion estimation or the motioncompensation is performed is placed so that a variation between acontrol point motion vector at a top left corner and a control pointmotion vector at a top right corner of the current block in the affinemotion compensation prediction falls within a predetermined range.

With this, the encoder can reduce the variation between the controlpoint motion vectors in affine motion compensation prediction, and thusthe affine motion compensation prediction is more likely to be selectedin the inter perdition. Accordingly motion compensation using affinemotion compensation can be efficiently performed.

Furthermore, for example, in the affine motion compensation prediction,the limit on the range within which the motion estimation or the motioncompensation is performed is newly determined for each current picture,or an appropriate set is selected for each current picture from among aplurality of predetermined sets of motion estimation ranges or aplurality of predetermined sets of motion compensation ranges.

With this, the limit on the range within which the motion estimation orthe motion compensation is performed can be placed at predeterminedintervals or using the predetermined sets, and thus it is possible toreduce the amount of processing, i.e. the memory bandwidth required forthe external memory.

Furthermore, for example, in the affine motion compensation prediction,the limit on the range within which the motion estimation or the motioncompensation is performed is changed in accordance with a type of areference picture.

With this, the limit on the range within which the motion estimation orthe motion compensation is performed can be placed at predeterminedintervals or using the predetermined sets, and thus it is possible toreduce the memory bandwidth required for the external memory.

Furthermore, for example, in the affine motion compensation prediction,the limit on the range within which the motion estimation or the motioncompensation is performed is determined for each predetermined profileand level.

With this, the limit on the range within which the motion estimation orthe motion compensation is performed can be determined for eachpredetermined profile and level, and thus it is possible to reduce thememory bandwidth required for the external memory.

Furthermore, for example, in the affine motion compensation prediction,the limit on the range within which the motion estimation or the motioncompensation is performed is determined in accordance withmotion-estimation processing power depending on computational processingpower on an encoder side or memory bandwidth.

With this, the limit on the range within which the motion estimation orthe motion compensation is performed can be determined in accordancewith the estimation processing power, and thus it is possible not onlyto reduce the amount of processing in accordance with the estimationprocessing power but also to efficiently perform motion compensationusing affine motion compensation.

Furthermore, for example, in the affine motion compensation prediction,the limit on the range within which the motion estimation or the motioncompensation is performed includes a limit on reference pictures inaddition to a limit on a range of referable pixels.

With this, it is possible not only to reduce the memory bandwidthrequired for the external memory but also to efficiently perform motioncompensation using affine motion compensation.

Furthermore, for example, in the affine motion compensation prediction,information about the limit on the range within which the motionestimation or the motion compensation is performed is included in headerinformation of a video parameter set (VPS), a sequence parameter set(SPS), or a picture parameter set (PPS) of an encoded bitstream.

With this, motion compensation using affine motion compensation can beefficiently performed.

Furthermore, for example, in the affine motion compensation prediction,the information about the limit on the range within which the motionestimation or the motion compensation is performed includes informationfor limiting reference pictures in addition to information for limitinga range of referable pixels.

With this, it is possible not only to reduce the memory bandwidthrequired for the external memory but also to efficiently perform motioncompensation using affine motion compensation.

Furthermore, for example, in the affine motion compensation prediction,in the motion estimation for affine inter mode, when a region referredto by a motion vector derived from a current control point motion vectorto be evaluated is outside the range within which the motion estimationis performed, the current control point motion vector is eliminated fromcandidates on which the motion estimation is performed.

With this, it is possible not only to reduce the memory bandwidthrequired for the external memory but also to efficiently perform motioncompensation using affine motion compensation.

Furthermore, for example, in the affine motion compensation prediction,in affine inter mode, when a region referred to by a motion vectorderived from a control point motion vector predictor obtained fromsurrounding encoded blocks neighboring the current block is outside therange within which the motion estimation is performed, encoding isprevented from being performed in the affine inter mode.

With this, it is possible not only to reduce the memory bandwidthrequired for the external memory but also to efficiently perform motioncompensation using affine motion compensation.

Furthermore, for example, in the affine motion compensation prediction,in affine merge mode, when a region referred to by a motion vectorderived from a control point motion vector obtained from surroundingencoded blocks neighboring the current block is outside the range withinwhich the motion compensation is performed, encoding is prevented frombeing performed in the affine merge mode.

With this, it is possible not only to reduce the memory bandwidthrequired for the external memory but also to efficiently perform motioncompensation using affine motion compensation.

Furthermore, for example, a decoder according to an aspect of thepresent disclosure includes circuitry and memory. Using the memory, thecircuitry, in affine motion compensation prediction in inter predictionfor a current block, places a limit on a range within which motionestimation or motion compensation is performed, and performs the motioncompensation for the current block to decode an encoded stream.

With this, the decoder can efficiently perform motion compensation usingaffine motion compensation. More specifically, a limit is placed on arange within which motion estimation or motion compensation is performedin affine motion compensation prediction, thereby allowing reduction inthe variation between control point motion vectors in affine motioncompensation prediction. Accordingly, the affine motion compensationprediction is more likely to be selected in the inter perdition, andthus the motion compensation can be efficiently performed using affinemotion compensation.

Here, for example, in the affine motion compensation prediction, thelimit on the range within which the motion estimation or the motioncompensation is performed is placed so that a variation between acontrol point motion vector at a top left corner and a control pointmotion vector at a top right corner of the current block in the affinemotion compensation prediction falls within a predetermined range.

With this, the decoder can reduce the variation between the controlpoint motion vectors in affine motion compensation prediction, and thusthe affine motion compensation prediction is more likely to be selectedin the inter perdition. Accordingly, motion compensation using affinemotion compensation can be efficiently performed.

Furthermore, for example, in the affine motion compensation prediction,the limit on the range within which the motion estimation or the motioncompensation is performed is newly determined for each current picture,or an appropriate set is selected for each current picture from among aplurality of predetermined sets of motion estimation ranges or aplurality of predetermined sets of motion compensation ranges.

With this, the limit on the range within which the motion estimation orthe motion compensation is performed can be placed at predeterminedintervals or using the predetermined sets, and thus it is possible toreduce the amount of processing, i.e. the memory bandwidth required forthe external memory.

Furthermore, for example, in the affine motion compensation prediction,the limit on the range within which the motion estimation or the motioncompensation is performed is changed in accordance with a type of areference picture.

With this, the limit on the range within which the motion estimation orthe motion compensation is performed can be placed at predeterminedintervals or using the predetermined sets, and thus it is possible toreduce the memory bandwidth required for the external memory.

Furthermore, for example, in the affine motion compensation prediction,the limit on the range within which the motion estimation or the motioncompensation is performed is determined for each predetermined profileand level.

With this, the limit on the range within which the motion estimation orthe motion compensation is performed can be determined for eachpredetermined profile and level, and thus it is possible to reduce thememory bandwidth required for the external memory.

Furthermore, for example, in the affine motion compensation prediction,the limit on the range within which the motion estimation or the motioncompensation is performed is determined in accordance with motionestimation processing power depending on computational processing poweron an encoder side or memory bandwidth.

With this, the limit on the range within which the motion estimation orthe motion compensation is performed can be determined in accordancewith the estimation processing power, and thus it is possible not onlyto reduce the memory bandwidth required for the external memory but alsoto efficiently perform motion compensation using affine motioncompensation.

Furthermore, for example, in the affine motion compensation prediction,the limit on the range within which the motion estimation or the motioncompensation is performed includes a limit, on reference pictures inaddition to a limit on a range of referable pixels.

With this, it is possible not only to reduce the memory bandwidthrequired for the external memory but also to efficiently perform motioncompensation using affine motion compensation.

Furthermore, for example, in the affine motion compensation prediction,information about the limit on the range within which the motionestimation or the motion compensation is performed is included in headerinformation of a video parameter set (VPS), a sequence parameter set(SPS), or a picture parameter set (PPS) of an encoded bitstream.

With this, motion compensation using affine motion compensation can beefficiently performed.

Furthermore, for example, in the affine motion compensation prediction,the information about the limit on the range within which the motionestimation or the motion compensation is performed includes informationfor limiting reference pictures in addition to information for limitinga range of referable pixels.

With this, it is possible not only to reduce the memory bandwidthrequired for the external memory but also to efficiently perform motioncompensation using affine motion compensation.

Furthermore, for example, in the affine motion compensation prediction,in the motion estimation for affine inter mode, when a region referredto by a motion vector derived from a current control point motion vectorto be evaluated is outside the range within which the motion estimationis performed, the current control point motion vector is eliminated fromcandidates on which the motion estimation is performed.

With this, it is possible not only to reduce the memory bandwidthrequired for the external memory but also to efficiently perform motioncompensation using affine motion compensation.

Furthermore, for example, in the affine motion compensation prediction,in affine inter mode, when a region referred to by a motion vectorderived from a control point, motion vector predictor obtained fromsurrounding decoded blocks neighboring the current block is outside therange within which the motion estimation is performed, encoding isprevented from being performed in the affine inter mode.

With this, it is possible not only to reduce the memory bandwidthrequired for the external memory but also to efficiently perform motioncompensation using affine motion compensation.

Furthermore, for example, in the affine motion compensation prediction,in affine merge mode, when a region referred to by a motion vectorderived from a control point motion vector obtained from surroundingdecoded blocks neighboring the current block is outside the range withinwhich the motion compensation is performed, encoding is prevented frombeing performed in the affine merge mode.

With this, it is possible not only to reduce the memory bandwidthrequired for the external memory but also to efficiently perform motioncompensation using affine motion compensation.

Furthermore, for example, an encoding method according to an aspect ofthe present disclosure includes in affine motion compensation predictionin inter prediction for a current block, placing a limit on a rangewithin which motion estimation or motion compensation is performed, andperforming the motion compensation for the current block.

With this, a device and others using the encoding method can efficientlyperform motion compensation using affine motion compensation. Morespecifically, a limit is placed on a range within which motionestimation or motion compensation is performed in affine motioncompensation prediction, thereby allowing reduction in the variationbetween control point motion vectors in affine motion compensationprediction. Accordingly, the affine motion compensation prediction ismore likely to be selected in the inter perdition, and thus the motioncompensation can be efficiently performed using affine motioncompensation. It is also possible to place a limit on the region of areference picture to be obtained, thereby having the possibility ofreducing the memory bandwidth required for an external memory, i.e. aframe memory.

Furthermore, for example, a decoding method according to an aspect ofthe present disclosure includes, in affine motion compensationprediction in inter prediction for a current block, placing a limit on arange within which motion estimation or motion compensation isperformed, and performing the motion compensation for the current blockto decode an encoded stream.

With this, a device and others using the decoding method can efficientlyperform motion compensation using affine motion compensation. Morespecifically, a limit is placed on a range within which motionestimation or motion compensation is performed in affine motioncompensation prediction, thereby allowing reduction in the variationbetween control point motion vectors in affine motion compensationprediction. Accordingly, the affine motion compensation prediction ismore likely to be selected in the inter perdition, and thus the motioncompensation can be efficiently performed using affine motioncompensation. It is also possible to place a limit on the region of areference picture to be obtained, thereby having the possibility ofreducing the memory bandwidth required for an external memory, i.e. aframe memory.

Furthermore, these general and specific aspects may be implemented usinga system, a device, a method, an integrated circuit, a computer program,a non-transitory computer readable recording medium such as a CD-ROM, orany combination of systems, devices, methods, integrated circuits,computer programs or recording media.

Hereinafter, embodiment(s) will be described with reference to thedrawings.

Note that the embodiment(s) described below each show a general orspecific example. The numerical values, shapes, materials, components,the arrangement and connection of the components, steps, order of thesteps, etc., indicated in the following embodiment(s) are mere examples,and therefore are not intended to limit the scope of the claims.Therefore, among the components in the following embodiment(s), thosenot recited in any of the independent claims defining the broadestinventive concepts are described as optional components.

Embodiment 1

First, an outline of Embodiment 1 will be presented. Embodiment 1 is oneexample of an encoder and a decoder to which the processes and/orconfigurations presented, in subsequent description of aspects of thepresent disclosure are applicable. Note that Embodiment 1 is merely oneexample of an encoder and a decoder to which the processes and/orconfigurations presented in the description of aspects of the presentdisclosure are applicable. The processes and/or configurations presentedin the description of aspects of the present disclosure can also beimplemented in an encoder and a decoder different from those accordingto Embodiment 1.

When the processes and/or configurations presented in the description ofaspects of the present disclosure are applied to Embodiment 1, forexample, any of the following may be performed.

(1) regarding the encoder or the decoder according to Embodiment 1,among components included in the encoder or the decoder according toEmbodiment 1, substituting a component, corresponding to a componentpresented in the description of aspects of the present disclosure with acomponent presented in the description of aspects of the presentdisclosure;

(2) regarding the encoder or the decoder according to Embodiment 1,implementing discretionary changes to functions or implemented,processes performed by one or more components included in the encoder orthe decoder according to Embodiment 1, such as addition, substitution,or removal, etc., of such functions or implemented processes, thensubstituting a component corresponding to a component presented in thedescription of aspects of the present disclosure with a componentpresented in the description of aspects of the present disclosure;

(3) regarding the method implemented by the encoder or the decoderaccording to Embodiment 1, implementing discretionary changes such asaddition of processes and/or substitution, removal of one or more of theprocesses included in the method, and then substituting a processescorresponding to a process presented in the description of aspects ofthe present disclosure with a process presented in the description ofaspects of the present disclosures;

(4) combining one or more components included in the encoder or thedecoder according to Embodiment 1 with a component presented in thedescription of aspects of the present disclosure, a component includingone or more functions included in a component presented in thedescription of aspects of the present disclosure, or a component thatimplements one or more processes implemented by a component presented inthe description of aspects of the present disclosure;

(5) combining a component including one or more functions included inone or more components included in the encoder or the decoder accordingto Embodiment 1, or a component that implements one or more processesimplemented by one or more components included in the encoder or thedecoder according to Embodiment 1 with a component presented in thedescription of aspects of the present disclosure, a component includingone or more functions included in a component presented in thedescription of aspects of the present disclosure, or a component thatimplements one or more processes implemented by a component presented inthe description of aspects of the present disclosure;

(6) regarding the method implemented by the encoder or the decoderaccording to Embodiment 1, among processes included in the method,substituting a process corresponding to a process presented in thedescription of aspects of the present disclosure with a processpresented in the description of aspects of the present disclosure; and

(7) combining one or more processes included in the method implementedby the encoder or the decoder according to Embodiment 1 with a processpresented in the description of aspects of the present disclosure.

Note that the implementation of the processes and/or configurationspresented in the description of aspects of the present disclosure is notlimited to the above examples. For example, the processes and/orconfigurations presented in the description of aspects of the presentdisclosure may be implemented in a device used for a purpose differentfrom the moving picture/picture encoder or the moving picture/picturedecoder disclosed in Embodiment 1. Moreover, the processes and/orconfigurations presented in the description of aspects of the presentdisclosure may be independently implemented. Moreover, processes and/orconfigurations described in different aspects may be combined.

[Encoder Outline]

First, the encoder according to Embodiment 1 will be outlined. FIG. 1 isa block diagram illustrating a functional configuration of encoder 100according to Embodiment 1. Encoder 100 is a moving picture/pictureencoder that encodes a moving picture/picture block by block.

As illustrated in FIG. 1, encoder 100 is a device that encodes a pictureblock by block, and includes splitter 102, subtractor 104, transformer106, quantizer 108, entropy encoder 110, inverse quantizer 112, inversetransformer 114, adder 116, block memory 118, loop filter 120, framememory 122, intra predictor 124, inter predictor 126, and predictioncontroller 128.

Encoder 100 is realized as, for example, a generic processor and memory.In this case, when a software program stored in the memory is executedby the processor, the processor functions as splitter 102, subtractor104, transformer 106, quantizer 108, entropy encoder 110, inversequantizer 112, inverse transformer 114, adder 116, loop filter 120,intra predictor 124, inter predictor 126, and prediction controller 128.Alternatively, encoder 100 may be realized as one or more dedicatedelectronic circuits corresponding to splitter 102, subtractor 104,transformer 106, quantizer 108, entropy encoder 110, inverse quantizer112, inverse transformer 114, adder 116, loop filter 120, intrapredictor 124, inter predictor 126, and prediction controller 128.

Hereinafter, each component included in encoder 100 will be described.

[Splitter]

Splitter 102 splits each picture included in an input moving pictureinto blocks, and outputs each block to subtracter 104. For example,splitter 102 first splits a picture into blocks of a fixed size (forexample, 128×128). The fixed size block is also referred to as codingtree unit (CTU). Splitter 102 then splits each fixed size block intoblocks of variable sizes (for example, 64×64 or smaller), based onrecursive quadtree and/or binary tree block splitting. The variable sizeblock is also referred to as a coding unit (CU), a prediction unit (PU),or a transform unit (TU). Note that in this embodiment, there is no needto differentiate between CU, PU, and TU; all or some of the blocks in apicture may be processed per CU, PU, or TU.

FIG. 2 illustrates one example of block splitting according toEmbodiment 1. In FIG. 2, the solid lines represent block boundaries ofblocks split by quadtree block splitting, and the dashed lines representblock boundaries of blocks split by binary tree block splitting.

Here, block 10 is a square 128×128 pixel block (128×128 block). This128×128 block 10 is first split into four square 64×64 blocks (quadtreeblock splitting).

The top left 64×64 block is further vertically split into two rectangle32×64 blocks, and the left 32×64 block is further vertically split intotwo rectangle 16×64 blocks (binary tree block splitting). As a result,the top left 64×64 block is split into two 16×64 blocks 11 and 12 andone 32×64 block 13.

The top right 64×64 block is horizontally split into two rectangle 64×32blocks 14 and 15 (binary tree block splitting).

The bottom left 64×64 block is first split into four square 32×32 blocks(quadtree block splitting). The top left block and the bottom rightblock among the four 32×32 blocks are further split. The top left 32×32block is vertically split into two rectangle 16×32 blocks, and the right16×32 block is further horizontally split into two 16×16 blocks (binarytree block splitting). The bottom right 32×32 block is horizontallysplit into two 32×16 blocks (binary tree block splitting). As a result,the bottom left 64×64 block is split into 16×32 block 16, two 16×16blocks 17 and 18, two 32×32 blocks 19 and 20, and two 32×16 blocks 21and 22.

The bottom right 64×64 block 23 is not split.

As described above, in FIG. 2, block 10 is split into 13 variable sizeblocks 11 through 23 based on recursive quadtree and binary tree blocksplitting. This type of splitting is also referred to as quadtree plusbinary tree (QTBT) splitting.

Note that in FIG. 2, one block is split into four or two blocks(quadtree or binary tree block splitting), but splitting is not limitedto this example. For example, one block may be split into three blocks(ternary block splitting). Splitting including such ternary blocksplitting is also referred to as multi-type tree (MBT) splitting.

[Subtractor]

Subtractor 104 subtracts a prediction signal (prediction sample) from anoriginal signal (original sample) per block split by splitter 102. Inother words, subtractor 104 calculates prediction errors (also referredto as residuals) of a block to be encoded (hereinafter referred to as acurrent block). Subtractor 104 then outputs the calculated predictionerrors to transformer 106.

The original signal is a signal input into encoder 100, and is a signalrepresenting an image for each picture included in a moving picture (forexample, a luma signal and two chroma signals). Hereinafter, a signalrepresenting an image is also referred to as a sample.

[Transformer]

Transformer 106 transforms spatial domain prediction errors intofrequency domain transform coefficients, and outputs the transformcoefficients to quantizer 108. More specifically, transformer 106applies, for example, a predefined discrete cosine transform (DCT) ordiscrete sine transform (DST) to spatial domain prediction errors.

Note that transformer 106 may adaptively select a transform type fromamong a plurality of transform types, and transform prediction errorsinto transform coefficients by using a transform basis functioncorresponding to the selected transform type. This sort of transform isalso referred to as explicit multiple core transform (EMT) or adaptivemultiple transform (AMT).

The transform types include, for example, DCT-II, DCT-V, DCT-VIII,DST-I, and DST-VII. FIG. 3 is a chart indicating transform basisfunctions for each transform type. In FIG. 3, N indicates the number ofinput pixels. For example, selection of a transform type from among theplurality of transform types may depend on the prediction type (intraprediction and inter prediction), and may depend on intra predictionmode.

Information indicating whether to apply such EMT or AMT (referred to as,for example, an AMT flag) and information indicating the selectedtransform type is signalled at the CU level. Note that the signaling ofsuch information need not be performed at the CU level, and may beperformed at another level (for example, at the sequence level, picturelevel, slice level, tile level, or CTU level).

Moreover, transformer 106 may apply a secondary transform to thetransform coefficients (transform result). Such a secondary transform isalso referred to as adaptive secondary transform (AST) or non-separablesecondary transform (NSST). For example, transformer 106 applies asecondary transform to each sub-block (for example, each 4×4 sub-block)included in the block of the transform coefficients corresponding to theintra prediction errors. Information indicating whether to apply NSSTand information related to the transform matrix used in NSST aresignalled at the CU level. Note that the signaling of such informationneed not be performed at the CU level, and may be performed at anotherlevel (for example, at the sequence level, picture level, slice level,tile level, or CTU level).

Here, a separable transform is a method in which a transform isperformed a plurality of times by separately performing a transform foreach direction according to the number of dimensions input. A nonseparable transform is a method of performing a collective transform inwhich two or more dimensions in a multidimensional input arecollectively regarded as a single dimension.

In one example of a non separable transform, when the input is a 4×4block, the 4×4 block is regarded as a single array including 16components, and the transform applies a 16×16 transform matrix to thearray.

Moreover, similar to above, after an input 4×4 block is regarded as asingle array including 16 components, a transform that performs aplurality of Givens rotations on the array (i.e., a Hypercube-GivensTransform) is also one example of a non-separable transform.

[Quantizer]

Quantizer 108 quantizes the transform coefficients output fromtransformer 106. More specifically, quantizer 108 scans, in apredetermined scanning order, the transform coefficients of the currentblock, and quantizes the scanned transform coefficients based onquantization parameters (QP) corresponding to the transformcoefficients. Quantizer 108 then outputs the quantized transformcoefficients (hereinafter referred to as quantized coefficients) of thecurrent block to entropy encoder 110 and inverse quantizer 112.

A predetermined order is an order for quantizing/inverse quantizingtransform coefficients. For example, a predetermined scanning order isdefined as ascending order of frequency (from low to high frequency) ordescending order of frequency (from high to low frequency).

A quantization parameter is a parameter defining a quantization stepsize (quantization width). For example, if the value of the quantizationparameter increases, the quantization step size also increases. In otherwords, if the value of the quantization parameter increases, thequantization error increases.

[Entropy Encoder]

Entropy encoder 110 generates an encoded signal (encoded bitstream) byvariable length encoding quantized coefficients, which are inputs fromquantizer 108. More specifically, entropy encoder 110, for example,binarizes quantized coefficients and arithmetic encodes the binarysignal.

[Inverse Quantizer]

Inverse quantizer 112 inverse quantizes quantized coefficients, whichare inputs from quantizer 108. More specifically, inverse quantizer 112inverse quantizes, in a predetermined scanning order, quantizedcoefficients of the current block. Inverse quantizer 112 then outputsthe inverse quantized transform coefficients of the current block toinverse transformer 114.

[Inverse Transformer]

Inverse transformer 114 restores prediction errors by inversetransforming transform coefficients, which are inputs from inversequantizer 112. More specifically, inverse transformer 114 restores theprediction errors of the current block by applying an inverse transformcorresponding to the transform applied by transformer 106 on thetransform coefficients. Inverse transformer 114 then outputs therestored prediction errors to adder 116.

Note that since information is lost in quantization, the restoredprediction errors do not match the prediction errors calculated bysubtractor 104. In other words, the restored prediction errors includequantization errors.

[Adder]

Adder 116 reconstructs the current block by summing prediction errors,which are inputs from inverse transformer 114, and prediction samples,which are inputs from prediction controller 128. Adder 116 then outputsthe reconstructed block to block memory 118 and loop filter 120. Areconstructed block is also referred to as a local decoded block.

[Block Memory]

Block memory 118 is storage for storing blocks in a picture to beencoded (hereinafter referred to as a current picture) for reference inintra prediction. More specifically, block memory 118 storesreconstructed blocks output from adder 116.

[Loop Filter]

Loop filter 120 applies a loop filter to blocks reconstructed by adder116, and outputs the filtered reconstructed blocks to frame memory 122.A loop filter is a filter used in an encoding loop (in-loop filter), andincludes, for example, a deblocking filter (DF), a sample adaptiveoffset (SAO), and an adaptive loop filter (ALF).

In ALF, a least square error filter for removing compression artifactsis applied. For example, one filter from among a plurality of filters isselected for each 2×2 sub-block in the current block based on directionand activity of local gradients, and is applied.

More specifically, first, each sub-block (for example, each 2×2 subblock) is categorized into one out of a plurality of classes (forexample, 15 or 25 classes). The classification of the sub-block is basedon gradient directionality and activity. For example, classificationindex C is derived based on gradient directionality D (for example, 0 to2 or 0 to 4) and gradient activity A (for example, 0 to 4) (for example,C=5D+A). Then, based on classification index C, each sub-block iscategorized into one out of a plurality of classes (for example, 15 or25 classes).

For example, gradient directionality D is calculated by comparinggradients of a plurality of directions (for example, the horizontal,vertical, and two diagonal directions). Moreover, for example, gradientactivity A is calculated by summing gradients of a plurality ofdirections and quantizing the sum.

The filter to be used for each sub-block is determined from among theplurality of filters based on the result of such categorization.

The filter shape to be used in ALF is, for example, a circular symmetricfilter shape. FIG. 4A through FIG. 40 illustrate examples of filtershapes used in ALF. FIG. 4A illustrates a 5×5 diamond shape filter, FIG.4B illustrates a 7×7 diamond shape filter, and FIG. 4C illustrates a 9×9diamond shape filter. Information indicating the filter shape issignalled at the picture level Note that the signaling of informationindicating the filter shape need not be performed at the picture level,and may be performed at another level (for example, at the sequencelevel, slice level, tile level, CTU level, or CU level).

The enabling or disabling of ALF is determined at the picture level orCU level. For example, for luma, the decision to apply ALF or not isdone at the CU level, and for chroma, the decision to apply ALF or notis done at the picture level. Information indicating whether ALF isenabled or disabled is signalled at the picture level or CU level Notethat the signaling of information indicating whether ALF is enabled ordisabled need not be performed at the picture level or CU level, and maybe performed at another level (for example, at the sequence level, slicelevel, tile level, or CTU level).

The coefficients set for the plurality of selectable filters (forexample, 15 or 25 filters) is signalled at the picture level Note thatthe signaling of the coefficients set need not be performed at thepicture level, and may be performed at another level (for example, atthe sequence level, slice level, tile level, CTU level, CU level, orsub-block level).

[Frame Memory]

Frame memory 122 is storage for storing reference pictures used in interprediction, and is also referred to as a frame buffer. Morespecifically, frame memory 122 stores reconstructed blocks filtered byloop filter 120.

[Intra Predictor]

Intra predictor 124 generates a prediction signal (intra predictionsignal) by intra predicting the current block with reference to a blockor blocks in the current picture and stored in block memory 118 (alsoreferred to as intra frame prediction). More specifically, intrapredictor 124 generates an intra prediction signal by intra predictionwith reference to samples (for example, luma and/or chroma values) of ablock or blocks neighboring the current block, and then outputs theintra prediction signal to prediction controller 128.

For example, intra predictor 124 performs intra prediction by using onemode from among a plurality of predefined intra prediction modes. Theintra prediction modes include one or more non*directional predictionmodes and a plurality of directional prediction modes.

The one or more non-directional prediction modes include, for example,planar prediction mode and DC prediction mode defined in theH.265/high-efficiency video coding (HEVC) standard (see H.265(ISO/IEC23008-2 HEVC(High Efficiency Video Coding))).

The plurality of directional prediction modes include, for example, the33 directional prediction modes defined in the H.265/HEVC standard. Notethat the plurality of directional prediction modes may further include32 directional prediction modes in addition to the 33 directionalprediction modes (for a total of 65 directional prediction modes). FIG.5A illustrates 67 intra prediction modes used in intra prediction (twonon-directional prediction modes and 65 directional prediction modes).The solid arrows represent the 33 directions defined in the H.265/HEVCstandard, and the dashed arrows represent the additional 32 directions.

Note that a luma block may be referenced in chroma block intraprediction. In other words, a chroma component of the current block maybe predicted based on a luma component of the current block. Such intraprediction is also referred to as cross-component linear model (CCLM)prediction. Such a chroma block intra prediction mode that references aluma block (referred to as, for example, CCLM mode) may be added as oneof the chroma block intra prediction modes.

Intra predictor 124 may correct post-intra-prediction pixel values basedon horizontal/vertical reference pixel gradients. Intra predictionaccompanied by this sort of correcting is also referred to as positiondependent intra prediction combination (PDPC). Information indicatingwhether to apply PDPC or not (referred to as, for example, a PDPC flag)is, for example, signalled at the CU level. Note that the signaling ofthis information need not be performed at the CU level, and may beperformed at another level (for example, on the sequence level, picturelevel, slice level, tile level, or CTU level).

[Inter Predictor]

Inter predictor 126 generates a prediction signal (inter predictionsignal) by inter predicting the current block with reference to a blockor blocks in a reference picture, which is different from the currentpicture and is stored in frame memory 122 (also referred to as interframe prediction). Inter prediction is performed per current block orper sub-block (for example, per 4×4 block) in the current block. Forexample, inter predictor 126 performs motion estimation in a referencepicture for the current block or sub-block. Inter predictor 126 thengenerates an inter prediction signal of the current block or sub-blockby motion compensation by using motion information (for example, amotion vector) obtained from motion estimation. Inter predictor 126 thenoutputs the generated inter prediction signal to prediction controller128.

The motion information used in motion compensation is signalled. Amotion vector predictor may be used for the signaling of the motionvector. In other words, the difference between the motion vector and themotion vector predictor may be signalled.

Note that the inter prediction signal may be generated using motioninformation for a neighboring block in addition to motion informationfor the current block obtained from motion estimation. Morespecifically, the inter prediction signal may be generated per sub blockin the current block by calculating a weighted sum of a predictionsignal based on motion information obtained from motion estimation and aprediction signal based on motion information for a neighboring block.Such inter prediction (motion compensation) is also referred to asoverlapped block motion compensation (OBMC).

In such an OBMC mode, information indicating sub-block size for OBMC(referred to as, for example, OBMC block size) is signalled at thesequence level. Moreover, information indicating whether to apply theOBMC mode or not (referred to as, for example, an OBMC flag) issignalled at the CU level Note that the signaling of such informationneed not be performed at the sequence level and CU level, and may beperformed at another level (for example, at the picture level, slicelevel, tile level, CTU level, or sub-block level).

Hereinafter, the OBMC mode will be described in further detail FIG. 5Bis a flowchart and FIG. 5C is a conceptual diagram for illustrating anoutline of a prediction image correction process performed via OBMCprocessing.

First, a prediction image (Pred) is obtained through typical motioncompensation using a motion vector (MV) assigned to the current block.

Next, a prediction image (Pred_L) is obtained by applying a motionvector (MV_L) of the encoded neighboring left block to the currentblock, and a first pass of the correction of the prediction image ismade by superimposing the prediction image and Pred_L.

Similarly, a prediction image (Pred_U) is obtained by applying a motionvector (MV_U) of the encoded neighboring upper block to the currentblock, and a second pass of the correction of the prediction image ismade by superimposing the prediction image resulting from the first passand Pred_U. The result of the second pass is the final prediction image.

Note that the above example is of a two-pass correction method using theneighboring left and upper blocks, but the method may be a three pass orhigher correction method that also uses the neighboring right and/orlower block.

Note that the region subject to superimposition may be the entire pixelregion of the block, and, alternatively, may be a partial block boundaryregion.

Note that here, the prediction image correction process is described asbeing based on a single reference picture, but the same applies when aprediction image is corrected based on a plurality of referencepictures. In such a case, after corrected prediction images resultingfrom performing correction based on each of the reference pictures areobtained, the obtained corrected prediction images are furthersuperimposed to obtain the final prediction image.

Note that, the unit of the current block may be a prediction block and,alternatively, may be a sub-block obtained by further dividing theprediction block.

One example of a method for determining whether to implement OBMCprocessing is by using an obmc_flag, which is a signal that indicateswhether to implement OBMC processing. As one specific example, theencoder determines whether the current block belongs to a regionincluding complicated motion. The encoder sets the obmc_flag to a valueof “1” when the block belongs to a region including complicated motionand implements OBMC processing when encoding, and sets the obmc_flag toa value of “1” when the block does not belong to a region includingcomplication motion and encodes without implementing OBMC processing.The decoder switches between implementing OBMC processing or not bydecoding the obmc_flag written in the stream and performing the decodingin accordance with the flag value.

Note that the motion information may be derived on the decoder sidewithout being signalled. For example, a merge mode defined in theH.265/HEVC standard may be used. Moreover, for example, the motioninformation may be derived by performing motion estimation on thedecoder side, in this case, motion estimation is performed without usingthe pixel values of the current block.

Here, a mode for performing motion estimation on the decoder side willbe described. A model for performing motion estimation on the decoderside is also referred to as pattern matched motion vector derivation(PMMVD) mode or frame rate up-conversion (FRUC) mode.

One example of FRUC processing is illustrated in FIG. 5D. First, acandidate list (a candidate list may be a merge list) of candidates eachincluding a motion vector predictor is generated with reference tomotion vectors of encoded blocks that spatially or temporally neighborthe current block. Next, the best candidate MV is selected from among aplurality of candidate MVs registered in the candidate list. Forexample, evaluation values for the candidates included in the candidatelist are calculated and one candidate is selected based on thecalculated evaluation values.

Next, a motion vector for the current block is derived from the motionvector of the selected candidate. More specifically, for example, themotion vector for the current block is calculated as the motion vectorof the selected candidate (best candidate MV), as-is. Alternatively, themotion vector for the current block may be derived by pattern matchingperformed in the vicinity of a position in a reference picturecorresponding to the motion vector of the selected candidate. In otherwords, when the vicinity of the best candidate MV is searched via thesame method and an MV having a better evaluation value is found, thebest candidate MV may be updated to the MV having the better evaluationvalue, and the MV having the better evaluation value may be used as thefinal MV for the current block. Note that a configuration in which thisprocessing is not implemented is also acceptable.

The same processes may be performed in cases in which the processing isperformed in units of sub-blocks.

Note that an evaluation value is calculated by calculating thedifference in the reconstructed image by pattern matching performedbetween a region in a reference picture corresponding to a motion vectorand a predetermined region. Note that the evaluation value may becalculated by using some other information in addition to thedifference.

The pattern matching used is either first pattern matching or secondpattern matching. First pattern matching and second pattern matching arealso referred to as bilateral matching and template matching,respectively.

In the first pattern matching, pattern matching is performed between twoblocks along the motion trajectory of the current block in two differentreference pictures. Therefore, in the first pattern matching, a regionin another reference picture conforming to the motion trajectory of thecurrent block is used as the predetermined region for theabove-described calculation of the candidate evaluation value.

FIG. 6 is for illustrating one example of pattern matching (bilateralmatching) between two blocks along a motion trajectory. As illustratedin FIG. 6, in the first pattern matching, two motion vectors (MV0, MV1)are derived by finding the best match between two blocks along themotion trajectory of the current block (Cur block) in two differentreference pictures (Ref0, Ref1). More specifically, a difference between(i) a reconstructed image in a specified position in a first encodedreference picture (Ref0) specified by a candidate MV and (ii) areconstructed picture in a specified position in a second encodedreference picture (Ref1) specified by a symmetrical MV scaled at adisplay time interval of the candidate MV may be derived, and theevaluation value for the current block may be calculated by using thederived difference. The candidate MV having the best evaluation valueamong the plurality of candidate MVs may be selected as the final MV.

Under the assumption of continuous motion trajectory, the motion vectors(MV0, MV1) pointing to the two reference blocks shall be proportional tothe temporal distances (TD0, TD1) between the current picture (Cur Pic)and the two reference pictures (Ref0), Ref1). For example, when thecurrent picture is temporally between the two reference pictures and thetemporal distance from the current picture to the two reference picturesis the same, the first pattern matching derives a mirror basedbi-directional motion vector.

In the second pattern matching, pattern matching is performed between atemplate in the current picture (blocks neighboring the current block inthe current picture (for example, the top and/or left neighboringblocks)) and a block in a reference picture. Therefore, in the secondpattern matching, a block neighboring the current block in the currentpicture is used as the predetermined region for the above-describedcalculation of the candidate evaluation value.

FIG. 7 is for illustrating one example of pattern matching (templatematching) between a template in the current picture and a block in areference picture. As illustrated in FIG. 7, in the second patternmatching, a motion vector of the current block is derived by searching areference picture (Ref0) to find the block that best matches neighboringblocks of the current block (Cur block) in the current picture (CurPic). More specifically, a difference between (i) a reconstructed imageof an encoded region that is both or one of the neighboring left andneighboring upper region and (ii) a reconstructed picture in the sameposition in an encoded reference picture (Ref0) specified by a candidateMV may be derived, and the evaluation value for the current block may becalculated by using the derived difference. The candidate MV having thebest evaluation value among the plurality of candidate MVs may beselected as the best candidate MV.

Information indicating whether to apply the FRUC mode or not (referredto as, for example, a FRUC flag) is signalled at the CU level. Moreover,when the FRUC mode is applied (for example, when the FRUC flag is set totrue), information indicating the pattern matching method (first patternmatching or second pattern matching) is signalled at the CU level. Notethat the signaling of such information need not be performed at the CUlevel, and may be performed at another level (for example, at thesequence level, picture level, slice level, tile level, CTU level, orsub-block level).

Here, a mode for deriving a motion vector based on a model assuminguniform linear motion will be described. This mode is also referred toas a bi-directional optical flow (BIO) mode.

FIG. 8 is for illustrating a model assuming uniform linear motion. InFIG. 8, (v_(x), v_(y)) denotes a velocity vector, and τ₀ and τ₁ denotetemporal distances between the current picture (Cur Pic) and tworeference pictures (Ref₀, Ref₁). (MVx₀, MVy₀) denotes a motion vectorcorresponding to reference picture Ref₀, and (MVx₁, MVy₁) denotes amotion vector corresponding to reference picture Ref₁.

Here, under the assumption of uniform linear motion exhibited byvelocity vector (v_(x), v_(y)), (MVx₀, MVy₀) and (MVx₁, MVy₁) arerepresented as (v_(x)τ₀, v_(y)τ₀) and (−v_(x)τ₁, −v_(y)τ₁),respectively, and the following optical flow equation is given.MATH. 1∂I ^((k)) /∂i+v _(x) ∂I ^((k)) /∂x+v _(y) ∂I ^((k)) /∂y=0  (1)

Here, 100 denotes a luma value from reference picture k (k=0, 1) aftermotion compensation. This optical flow equation shows that the sum of(i) the time derivative of the luma value, (ii) the product of thehorizontal velocity and the horizontal component of the spatial gradientof a reference picture, and (iii) the product of the vertical velocityand the vertical component of the spatial gradient of a referencepicture is equal to zero. A motion vector of each block obtained from,for example, a merge list is corrected pixel by pixel based on acombination of the optical flow equation and Hermite interpolation.

Note that a motion vector may be derived on the decoder side using amethod other than deriving a motion vector based on a model assuminguniform linear motion. For example, a motion vector may be derived foreach sub-block based on motion vectors of neighboring blocks.

Here, a mode in which a motion vector is derived for each sub-blockbased on motion vectors of neighboring blocks will be described. Thismode is also referred to as affine motion compensation prediction mode.

FIG. 9A is for illustrating deriving a motion vector of each sub-blockbased on motion vectors of neighboring blocks. In FIG. 9A, the currentblock includes 16 4×4 sub-blocks. Here, motion vector v₀ of the top leftcorner control point in the current block is derived based on motionvectors of neighboring sub-blocks, and motion vector v₁ of the top rightcorner control point in the current block is derived based on motionvectors of neighboring blocks. Then, using the two motion vectors v₀ andv₁, the motion vector (v_(x), v_(y)) of each sub-block in the currentblock is derived using Equation 2 below.

MATH.  2 $\begin{matrix}\left\{ \begin{matrix}{v_{x} = {{\frac{\left( {v_{1x} - v_{0x}} \right)}{w}x} - {\frac{\left( {v_{1y} - v_{0y}} \right)}{w}y} + v_{0x}}} \\{v_{y} = {{\frac{\left( {v_{1y} - v_{0y}} \right)}{w}x} + {\frac{\left( {v_{1x} - v_{0x}} \right)}{w}y} + v_{0y}}}\end{matrix} \right. & (2)\end{matrix}$

Here, x and y are the horizontal and vertical positions of thesub-block, respectively, and w is a predetermined weighted coefficient.

Such an affine motion compensation prediction mode may include a numberof modes of different methods of deriving the motion vectors of the topleft and top right corner control points. Information indicating such anaffine motion compensation prediction mode (referred to as, for example,an affine flag) is signalled at the CU level. Note that the signaling ofinformation indicating the affine motion compensation prediction modeneed not be performed at the CU level, and may be performed at anotherlevel (for example, at the sequence level, picture level, slice level,tile level, CTU level, or sub-block level).

[Prediction Controller]

Prediction controller 128 selects either the intra prediction signal orthe inter prediction signal, and outputs the selected prediction signalto subtractor 104 and adder 116.

Here, an example of deriving a motion vector via merge mode in a currentpicture will be given. FIG. 9B is for illustrating an outline of aprocess for deriving a motion vector via merge mode.

First, an MV predictor list in which candidate MV predictors areregistered in generated. Examples of candidate MV predictors include:spatially neighboring MV predictors, which are MVs of encoded blockspositioned in the spatial vicinity of the current block; a temporallyneighboring MV predictor, which is an MV of a block in an encodedreference picture that neighbors in the same location as the currentblock; a combined MV predictor, which is an MV generated by combiningthe MV values of the spatially neighboring MV predictor and thetemporally neighboring MV predictor; and a zero MV predictor, which isan MV whose value is zero.

Next, the MV of the current block is determined by selecting one MVpredictor from among the plurality of MV predictors registered in the MVpredictor list.

Furthermore, in the variable-length encoder, a merge_idx, which is asignal indicating which MV predictor is selected, is written and encodedinto the stream.

Note that the MV predictors registered in the MV predictor listillustrated in FIG. 9B constitute one example. The number of MVpredictors registered in the MV predictor list may be different from thenumber illustrated in FIG. 9B, the MV predictors registered in the MVpredictor list may omit one or more of the types of MV predictors givenin the example in FIG. 9B, and the MV predictors registered in the MVpredictor list may include one or more types of MV predictors inaddition to and different from the types given in the example in FIG.9B.

Note, that the final MV may be determined by performing DMVR processing(to be described later) by using the MV of the current block derived viamerge mode.

Here, an example of determining an MV by using DMVR processing will begiven.

FIG. 9C is a conceptual diagram for illustrating an outline of DMVRprocessing.

First, the most appropriate MVP set for the current block is consideredto be the candidate MV, reference pixels are obtained from a firstreference picture, which is a picture processed in the L0 direction inaccordance with the candidate MV, and a second reference picture, whichis a picture processed in the L1 direction in accordance with thecandidate MV, and a template is generated by calculating the average ofthe reference pixels.

Next, using the template, the surrounding regions of the candidate MVsof the first and second reference pictures are searched, and the MV withthe lowest cost is determined to be the final MV. Note that the costvalue is calculated using, for example, the difference between eachpixel value in the template and each pixel value in the regionssearched, as well as the MV value.

Note that the outlines of the processes described here are fundamentallythe same in both the encoder and the decoder.

Note that processing other than the processing exactly as describedabove may be used, so long as the processing is capable of deriving thefinal MV by searching the surroundings of the candidate MV.

Here, an example of a mode that generates a prediction image by usingLIC processing will be given.

FIG. 9D is for illustrating an outline of a prediction image generationmethod using a luminance correction process performed via LICprocessing.

First, an MV is extracted for obtaining, from an encoded referencepicture, a reference image corresponding to the current block.

Next, information indicating how the luminance value changed between thereference picture and the current picture is extracted and a luminancecorrection parameter is calculated by using the luminance pixel valuesfor the encoded left neighboring reference region and the encoded upperneighboring reference region, and the luminance pixel value in the samelocation in the reference picture specified by the MV.

The prediction image for the current block is generated by performing aluminance correction process by using the luminance correction parameteron the reference image in the reference picture specified by the MV.

Note that the shape of the surrounding reference region illustrated inFIG. 9D is just one example; the surrounding reference region may have adifferent shape.

Moreover, although a prediction image is generated from a singlereference picture in this example, in cases in which a prediction imageis generated from a plurality of reference pictures as well, theprediction image is generated after performing a luminance correctionprocess, via the same method, on the reference images obtained from thereference pictures.

One example of a method for determining whether to implement LICprocessing is by using anlic_flag, which is a signal that indicateswhether to implement LIC processing. As one specific example, theencoder determines whether the current block belongs to a region ofluminance change. The encoder sets the lic_flag to a value of “1” whenthe block belongs to a region of luminance change and implements LICprocessing when encoding, and sets the lic_flag to a value of “0” whenthe block does not belong to a region of luminance change and encodeswithout implementing LIC processing. The decoder switches betweenimplementing LIC processing or not by decoding the lic_flag written inthe stream and performing the decoding in accordance with the flagvalue.

One example of a different method of determining whether to implementLIC processing is determining so in accordance with whether LICprocessing was determined to be implemented for a surrounding block. Inone specific example, when merge mode is used on the current block,whether LIC processing was applied in the encoding of the surroundingencoded block selected upon deriving the MV in the merge mode processingmay be determined, and whether to implement LIC processing or not can beswitched based on the result of the determination. Note that in thisexample, the same applies to the processing performed on the decoderside.

[Decoder Outline]

Next, a decoder capable of decoding an encoded signal (encodedbitstream) output from encoder 100 will be described. FIG. 10 is a blockdiagram illustrating a functional configuration of decoder 200 accordingto Embodiment 1. Decoder 200 is a moving picture/picture decoder thatdecodes a moving picture/picture block by block.

As illustrated in FIG. 10, decoder 200 includes entropy decoder 202,inverse quantizer 204, inverse transformer 206, adder 208, block memory210, loop filter 212, frame memory 214, intra predictor 216, interpredictor 218, and prediction controller 220.

Decoder 200 is realized as, for example, a generic processor and memory.In this case, when a software program stored in the memory is executedby the processor, the processor functions as entropy decoder 202,inverse quantizer 204, inverse transformer 206, adder 208, loop filter212, intra predictor 216, inter predictor 218, and prediction controller220. Alternatively decoder 200 may be realized as one or more dedicatedelectronic circuits corresponding to entropy decoder 202, inversequantizer 204, inverse transformer 206, adder 208, loop filter 212,intra predictor 216, inter predictor 218, and prediction controller 220.

Hereinafter, each component included in decoder 200 will be described.

[Entropy Decoder]

Entropy decoder 202 entropy decodes an encoded bitstream. Morespecifically for example, entropy decoder 202 arithmetic decodes anencoded bitstream into a binary signal. Entropy decoder 202 thendebinarizes the binary signal. With this, entropy decoder 202 outputsquantized coefficients of each block to inverse quantizer 204.

[Inverse Quantizer]

Inverse quantizer 204 inverse quantizes quantized coefficients of ablock to be decoded (hereinafter referred to as a current block), whichare inputs from entropy decoder 202. More specifically, inversequantizer 204 inverse quantizes quantized coefficients of the currentblock based on quantization parameters corresponding to the quantizedcoefficients. Inverse quantizer 204 then outputs the inverse quantizedcoefficients (i.e., transform coefficients) of the current block toinverse transformer 206.

[Inverse Transformer]

Inverse transformer 206 restores prediction errors by inversetransforming transform coefficients, which are inputs from inversequantizer 204.

For example, when information parsed from an encoded bitstream indicatesapplication of EMT or AMT (for example, when the AMT flag is set totrue), inverse transformer 206 inverse transforms the transformcoefficients of the current block based on information indicating theparsed transform type.

Moreover, for example, when information parsed from an encoded bitstreamindicates application of NSST, inverse transformer 206 applies asecondary inverse transform to the transform coefficients.

[Adder]

Adder 208 reconstructs the current block by summing prediction errors,which are inputs from inverse transformer 206, and prediction samples,which is an input from prediction controller 220. Adder 208 then outputsthe reconstructed block to block memory 210 and loop filter 212.

[Block Memory]

Block memory 210 is storage for storing blocks in a picture to bedecoded (hereinafter referred to as a current picture) for reference inintra prediction. More specifically, block memory 210 storesreconstructed blocks output from adder 208.

[Loop Filter]

Loop filter 212 applies a loop filter to blocks reconstructed by adder208, and outputs the filtered reconstructed blocks to frame memory 214and, for example, a display device.

When information indicating the enabling or disabling of ALF parsed froman encoded bitstream indicates enabled, one filter from among aplurality of filters is selected based on direction and activity oflocal gradients, and the selected filter is applied to the reconstructedblock.

[Frame Memory]

Frame memory 214 is storage for storing reference pictures used in interprediction, and is also referred to as a frame buffer. Morespecifically, frame memory 214 stores reconstructed blocks filtered byloop filter 212.

[Intra Predictor]

Intra predictor 216 generates a prediction signal (intra predictionsignal) by intra prediction with reference to a block or blocks in thecurrent picture and stored in block memory 210. More specifically, intrapredictor 216 generates an intra prediction signal by intra predictionwith reference to samples (for example, luma and/or chroma values) of ablock or blocks neighboring the current block, and then outputs theintra prediction signal to prediction controller 220.

Note that when an intra prediction mode in which a chroma block is intrapredicted from a luma block is selected, intra predictor 216 may predictthe chroma component of the current block based on the luma component ofthe current block.

Moreover, when information indicating the application of PDPC is parsedfrom an encoded bitstream, intra predictor 216 corrects postintra-prediction pixel values based on horizontal/vertical referencepixel gradients.

[Inter Predictor]

Inter predictor 218 predicts the current block with reference to areference picture stored in frame memory 214. Inter prediction isperformed per current block or per sub-block (for example, per 4×4block) in the current block. For example, inter predictor 218 generatesan inter prediction signal of the current block or sub-block by motioncompensation by using motion information (for example, a motion vector)parsed from an encoded bitstream, and outputs the inter predictionsignal to prediction controller 220.

Note that when the information parsed from the encoded bitstreamindicates application of OBMC mode, inter predictor 218 generates theinter prediction signal using motion information for a neighboring blockin addition to motion information for the current block obtained frommotion estimation.

Moreover, when the information parsed from the encoded bitstreamindicates application of FRUC mode, inter predictor 218 derives motioninformation by performing motion estimation in accordance with thepattern matching method (bilateral matching or template matching) parsedfrom the encoded bitstream. Inter predictor 218 then performs motioncompensation using the derived motion information.

Moreover, when BIO mode is to be applied, inter predictor 218 derives amotion vector based on a model assuming uniform linear motion. Moreover,when the information parsed from the encoded bitstream indicates thataffine motion compensation prediction mode is to be applied, interpredictor 218 derives a motion vector of each sub-block based on motionvectors of neighboring blocks.

[Prediction Controller]

Prediction controller 220 selects either the intra prediction signal orthe inter prediction signal, and outputs the selected prediction signalto adder 208.

[Description of Affine Inter Mode of Affine Motion CompensationPrediction]

As described above, a mode for deriving a motion vector of eachsub-block based on motion vectors of neighboring blocks is referred toas affine motion compensation prediction mode. The affine motioncompensation prediction mode includes two modes: affine inter mode; andaffine merge mode. Hereinafter, the two modes: affine inter mode; andaffine merge mode, will be described.

FIG. 11 is a conceptual diagram for illustrating affine inter mode ofaffine motion compensation prediction. FIG. 11 shows a current block,motion vector predictor v₀ of the top left corner control point of thecurrent block, and motion vector predictor v₁ of the top right cornercontrol point of the current block.

In affine inter mode, as shown in FIG. 11, motion vector predictor v₀ ofthe top left corner control point is selected from among motion vectorsof blocks A, B, and C which are surrounding encoded blocks neighboringthe current block. In the same manner, motion vector predictor v₁ of thetop right corner control point is selected from among motion vectors ofblocks D and E which are surrounding encoded blocks neighboring thecurrent block.

In the encoding, based on the surrounding encoded blocks neighboring thecurrent block, it is determined, using cost evaluation, etc., whichmotion vector of an encoded block is selected as the motion vectorpredictor of the control point in affine motion compensation predictionfor the current block. Subsequently, a flag indicating which motionvector of an encoded block is selected is written in the streamed themotion vector predictor of the control point.

Furthermore, in the encoding, after the motion vector predictor of thecontrol point in the current block is determined, motion estimation isperformed to estimate the motion vector of the control point. Using theestimated motion vector of the control point, an affine motion vector ofeach sub-block in the current block is calculated from Equation 2 asdescribed above, and motion compensation is performed. While the motioncompensation is performed, a difference between the estimated motionvector of the control point and the motion vector predictor of thecontrol point is written in the stream.

Note that the foregoing describes the operation of the encoding, but thesame is true of the operation of the decoding.

[Description of Affine Merge Mode of Affine Motion CompensationPrediction]

FIGS. 12A and 12B are each a conceptual diagram for illustrating affinemerge mode of affine motion compensation prediction. FIG. 12A shows acurrent block, and blocks A to D which are surrounding encoded blocksneighboring the current block. FIG. 12B shows a processing example ofaffine merge mode of affine motion compensation prediction. FIG. 12Balso shows the current block, motion vector predictor v₀ of the top leftcorner control point, motion vector predictor v₁ of the top right cornercontrol point, and block A which is an encoded block.

In affine merge mode, as shown in FIG. 12A, the surrounding encodedblocks neighboring the current block are checked in the following order:block A (left), block B (top), block C (top right), block D (bottomleft), and block E (top left). Subsequently, the first effective encodedblock which is encoded using affine motion compensation prediction isidentified from among the surrounding encoded blocks A through D.

For example, referring to FIG. 12B, when encoded block A neighboring thecurrent block to the left is encoded using affine motion compensationprediction, motion vector v₂ at the top left corner, motion vector v₃ atthe top right corner, and motion vector v₄ at the bottom left corner ofthe encoded block including block A are derived. Next, motion vector v₀of the top left corner control point of the current block is derivedfrom derived motion vectors v₂, v₃, and v₄. In the same manner, motionvector v₁ of the top right corner control point of the current block isderived.

Next, using derived motion vector v₀ of the top left corner controlpoint and motion vector v₁ of the top right corner control point of thecurrent block, an affine motion vector of each sub-block in the currentblock is calculated from Equation 2, and motion compensation isperformed.

Note that the foregoing describes the operation of the encoding, but thesame is true of the operation of the decoding.

[Internal Configuration of Affine Motion Compensation Prediction inInter Predictor in Encoder]

FIG. 13 is a block diagram illustrating an internal configuration foraffine motion compensation prediction in inter predictor 126 included inencoder 100 according to Embodiment 1. Note that the following focuseson the operation of inter predictor 126 included in encoder 100, but thesame is true of the operation of inter predictor 218 included in decoder200.

As shown in FIG. 13, inter predictor 126 according to Embodiment 1includes range determiner 1261, control point MV deriver 1262, affine MVcalculator 1263, motion compensation unit 1264, and motion estimationunit 1265.

Range determiner 1261 determines a range of motion estimation or motioncompensation in a reference picture based on range limit information ofmotion estimation or motion compensation indicating a partial region inthe reference picture within which motion estimation or motioncompensation is allowed. The determined range of motion estimation ormotion compensation limits a region in the reference picture withinwhich motion estimation or motion compensation in affine motioncompensation prediction is allowed. Thus, the possible range of themotion vector (MV) selected in affine motion compensation prediction islimited by placing a limit on the region in the reference picture withinwhich motion estimation or motion compensation is allowed.

In affine inter mode or affine merge mode of affine motion compensationprediction, control point MV deriver 1262 derives the motion vector ofthe control point (hereinafter, referred to as control point MV) usingthe MVs of the surrounding encoded blocks neighboring the current block.

Affine MV calculator 1263 calculates an affine motion vector(hereinafter, referred to as affine MV) for each sub-block from Equation2 using the control point MVs derived by control point MV deriver 1262.

Motion compensation unit 1264 generates a prediction image by performingmotion compensation using the affine MV calculated for each sub-block byaffine MV calculator 1263.

In affine inter mode, motion estimation unit 1265 performs motionestimation through cost evaluation using a current image and theprediction image provided from motion compensation unit 1264. In doingso, when the affine MV is outside the range of motion estimation andmotion compensation in the reference picture, affine inter mode andaffine merge mode using the derived control point MVs are prevented.

[First Processing Procedure for Affine Inter Mode]

FIG. 14 is a flow chart for illustrating the first processing procedurefor affine inter mode of affine motion compensation performed by interpredictor 126 in encoder 100 according to Embodiment 1.

As shown in FIG. 14, firstly, inter-picture predictor 126 determines arange of motion estimation within which motion estimation is allowed,based on the range limit information of motion estimation indicating apartial region in the reference picture within which motion estimationis allowed (S101).

Next, inter-picture predictor 126 obtains the motion vectors (MVs) ofthe surrounding encoded blocks neighboring the current block, andderives the motion vector predictor of the control point (hereinafter,referred to as control point MV predictor) using the obtained MVs(S102). In affine inter mode, as described with reference to FIG. 11,the motion vectors (MVs) of the surrounding encoded blocks neighboringthe current block are obtained, and the control point MV predictor isderived using the obtained MVs. Here, a flag indicating which MV is usedfrom among the MVs is written in the stream.

Next, while updating the motion vector of the control point(hereinafter, referred to as control point MV) (S103), interpicturepredictor 126 calculates an affine MV for each sub-block from Equation 2(S104).

In doing so, inter-picture predictor 126 determines whether the affineMV calculated at step S104 is within the range of motion estimation(S105). When it is determined to be outside the range (outside the rangeat S105), interpicture predictor 126 eliminates a current control pointMV to be evaluated from search candidates.

On the other hand, when it is determined to be within the range (withinthe range at S105), interpicture predictor 126 performs affine motioncompensation (S106), and searches the control point MV having a minimumcost value (for example, a minimum difference value between the currentimage and the prediction image). Here, a difference value between thecontrol point MV obtained through the search and the control point MVupdated at step S103 is written in the stream. For example, the obtainedcontrol point MV is set to the control point MV at the start of thesearch, and thereby a value closer to the optimal value can be set as aninitial value of the search. Accordingly, the accuracy of the search canbe improved.

Note that when surrounding pixels of the current block are used in aprocess following the affine motion compensation prediction (forexample, OBMC) and a region including the surrounding pixels used in theprocess following the affine motion compensation prediction is outsidethe range of motion estimation, the derived control point MV may beeliminated from the search candidates.

Furthermore, inter predictor 218 in decoder 200 performs decoding basedon information of the bitstream generated by encoder 100 in theforegoing manner, and thereby the affine motion compensation can beperformed in affine inter mode within the limited range of motionestimation.

[Second Processing Procedure for Affine Inter Mode]

FIG. 15 is a flow chart for illustrating the second processing procedurefor affine inter mode of affine motion compensation performed by interpredictor 120 in encoder 100 according to Embodiment 1. The samecomponents as those in FIG. 14 are assigned with the same referencesigns, and redundant descriptions will be omitted. The second processingprocedure shown in FIG. 15 differs from the first processing procedureshown in FIG. 14 in that it is determined based on not the affine MV butthe control point MV whether the current control point MV to beevaluated is eliminated from the search candidates.

More specifically, at step S107, interpicture predictor 126 determineswhether a variation in value between two control point MVs to beevaluated, i.e. the top left corner control point MV and the top rightcorner control point MV, is within the limited range. When it isdetermined to be outside the range (outside the range at S107),interpicture predictor 126 eliminates the current control point MV to beevaluated from the search candidates. Here, for example, the variationin value between the two control point MVs means a difference in size ordirection, temporal distance to a reference picture, or a differencevalue between the two control point MVs. For example, the position inthe reference picture referred to by the two control point MVs, i.e. thetop left corner control point MV and the top right corner control pointMV, is within the limited range.

The affine MV for each sub-block is calculated from Equation 2 using thecontrol point MVs at step S104, and thus a large variation between thetwo control point MVs leads to a large variation between the calculatedaffine MVs, thereby exceeding the range of motion estimation. Incontrast, when the variation between the two control point MVs is withina specified range, the calculated affine MV falls within the range ofmotion estimation. Accordingly, the specified range is determined inadvance as the limited range at step S101, and thereby upon updating thecontrol point MV, the derived control point MV can be eliminated fromthe search candidates to reduce the amount of processing.

Note that when a variation between control point MV predictors isdetermined to have already exceeded the limited range in the deriving ofthe control point MV predictor at step S102, inter picture predictor 126may prevent encoding from being performed in affine inter mode.

Furthermore, when surrounding pixels of the current block are used in aprocess following the affine motion compensation prediction (forexample, OBMC) and a region including the surrounding pixels used in theprocess following the affine motion compensation prediction is outsidethe range of motion estimation, the derived control point MV may beeliminated from the search candidates.

Furthermore, inter predictor 218 in decoder 200 performs decoding basedon information of the bitstream generated by encoder 100 in theforegoing manner, and thereby the affine motion compensation can beperformed in affine inter mode within the limited range of motionestimation.

[First Processing Procedure for Affine Merge Mode]

FIG. 16 is a flow chart for illustrating the first processing procedurefor affine merge mode of affine motion compensation performed by interpredictor 126 in encoder 100 according to Embodiment 1.

As shown in FIG. 16, firstly, interpicture predictor 126 determines arange of motion compensation within which motion compensation isallowed, based on the range limit information of motion compensationindicating a partial region in the reference picture within which motioncompensation is allowed (S201).

Next, inter-picture predictor 126 checks surrounding encoded blocksneighboring the current block in a predetermined order. Subsequently,inter-picture predictor 126 selects the MV of the first effectiveencoded block which is encoded using affine motion compensationprediction, and derives the control point MV using the selected MV(S202). In affine merge mode, as described with reference to FIG. 12A,the surrounding encoded blocks neighboring the current block are checkedin the following order: block A (left), block B (top), block C (topright), block D (bottom left), and block E (top left) which are thesurrounding encoded blocks neighboring the current block. Subsequently,the MV of the first effective encoded block which is encoded usingaffine motion compensation prediction is selected from the surroundingencoded blocks neighboring the current block, and the control point MVis derived using the selected MV.

Next, inter picture predictor 126 calculates an affine MV for eachsub-block from equation 2 using the control point MVs derived at stepS202 (S203).

In doing so, inter picture predictor 126 determines whether the affineMV calculated at step S203 is within the range of motion compensation(S204). When it is determined to be outside the range (outside the rangeat S204), interpicture predictor 126 prevents encoding from beingperformed in affine merge mode (S205).

On the other hand, when it is determined to be within the range (withinthe range at S204), inter picture predictor 126 performs affine motioncompensation (S206) to obtain the prediction image.

Note that when surrounding pixels of the current block are used in aprocess following the affine motion compensation prediction (forexample, OBMC) and a region including the surrounding pixels used in theprocess following the affine motion compensation prediction is outsidethe range of motion compensation, encoding may be prevented from beingperformed in affine merge mode.

Furthermore, inter predictor 218 in decoder 200 performs decoding basedon information of the bitstream generated by encoder 100 in theforegoing manner, and thereby the affine motion compensation can beperformed in affine merge mode within the limited range of motioncompensation.

[Second Processing Procedure for Affine Merge Mode]

FIG. 17 is a flow chart for illustrating the second processing procedurefor affine merge mode of affine motion compensation performed by interpredictor 126 in encoder 100 according to Embodiment 1. The samecomponents as those in FIG. 16 are assigned with the same referencesigns, and redundant descriptions will be omitted. The second processingprocedure shown in FIG. 17 differs from the first processing procedureshown in FIG. 16 in that it is determined based on not the affine MV butthe control point MV whether a current control point MV to be evaluatedis eliminated from the search candidates.

More specifically, at step S207, inter picture predictor 126 determineswhether a variation in value between two control point MVs to beevaluated, i.e. the top left corner control point MV and the top rightcorner control point MV, is within the limited range. When it isdetermined to be outside the range (outside the range at S207), theprocessing proceeds to step S205 and the encoding is prevented frombeing performed in affine merge mode. Here, for example, the variationin value between the two control point MVs means a difference in size ordirection, temporal distance to a reference picture, or a differencevalue between the two control point MVs. For example, the position inthe reference picture referred to by the two control point MVs, i.e. thetop left corner control point MV and the top right corner control pointMV, is within the limited range.

The affine MV for each sub-block is calculated from Equation 2 using thecontrol point MVs at step S203, and thus a large variation between thetwo control point MVs leads to a large variation between the calculatedaffine MVs, thereby exceeding the range of motion estimation. Incontrast, when the variation between the two control point MVs is withina specified range, the calculated affine MV falls within the range ofmotion estimation. Accordingly, the specified range is determined inadvance as the limited range at step S201, and thereby upon deriving thecontrol point MV, the encoding can be prevented from being performed inaffine merge mode to reduce the amount of processing.

Note that when surrounding pixels of the current block are used in aprocess following the affine motion compensation prediction (forexample, OBMC) and a region including the surrounding pixels used in theprocess following the affine motion compensation prediction is outsidethe range of motion compensation, encoding may be prevented from beingperformed in affine merge mode.

Furthermore, inter predictor 218 in decoder 200 performs decoding basedon information of the bitstream generated by encoder 100 in theforegoing manner, and thereby the affine motion compensation can beperformed in affine merge mode within the limited range of motioncompensation.

Advantageous Effects of Embodiment 1

According to Embodiment 1, a limit is placed on the range of motionvectors, thereby allowing reduction in the variation between controlpoint motion vectors in affine motion compensation prediction.Accordingly, the affine motion compensation prediction is more likely tobe selected in the inter perdition. It is also possible to place a limiton the region of a reference picture to be obtained, thereby having thepossibility of reducing the memory bandwidth required for an externalmemory, i.e. a frame memory.

For example, assuming that the range of motion estimation can beunlimitedly and broadly defined, the size and direction of the motionvector for each block in a picture may vary in a wide range.Furthermore, the affine motion compensation is intended for parallelmotion and linear transformation such as scaling, shearing, or rotationof an object in the picture, and thus when the affine motioncompensation prediction is selected, it is expected that two controlpoint motion vectors, i.e. the top left corner control point MV and thetop right corner control point MV, are more likely to have the samedirection. However, when the size and direction of the motion vector foreach block in the picture vary in a wide range, the motion vectorselected from surrounding encoded blocks neighboring the current blockmay also vary. This leads to the variation in the size and directionbetween the affine motion vectors, and thus the affine motioncompensation prediction would be less likely to be selected.Furthermore, when the size and direction of the motion vector for eachblock in the picture vary in a wide range, the region in the picture tobe obtained as a reference image is also expanded. Accordingly, thememory bandwidth required for an external memory, i.e. a frame memory ismore likely to increase.

Note that in the affine motion compensation prediction performed byinter predictor 126 in encoder 100, the following is achieved by placinga limit on the possible range of MVs. In other words, also in interpredictor 218 in decoder 200 that decodes the encoded bitstreamgenerated by encoder 100, the possible range of motion vectors in theaffine motion compensation prediction is limited in the same manner asencoder 100.

Furthermore, all the components described in Embodiment 1 are notnecessarily required. Only some of the components in Embodiment 1 may beincluded. Furthermore, the processing of all the components described inEmbodiment 1 is not limited to this. Components other than thecomponents in Embodiment 1 may be included to perform the processing.

Variation 1

Note that in the affine motion compensation prediction, the motionestimation range or the motion compensation range may be newlydetermined for each current picture, or an appropriate set may beselected for each current picture from among a plurality ofpredetermined sets of motion estimation ranges or a plurality ofpredetermined sets of motion compensation ranges. With this, thevariation between the control point motion vectors in affine motioncompensation prediction can be reduced, and thus the affine motioncompensation prediction is more likely to be selected in the interperdition. Accordingly, motion compensation using affine motioncompensation can be efficiently performed.

Furthermore, in the affine motion compensation prediction, the motionestimation range or the motion compensation range may be changed inaccordance with a type of a reference picture. For example, in referringto P picture, the motion estimation range or the motion compensationrange may be larger than that interfering to B picture. Furthermore, inthe affine motion compensation prediction, the motion estimation rangeor the motion compensation range may be determined for eachpredetermined profile and level. With this, the limit on the rangewithin which the motion estimation or the motion compensation isperformed is appropriately determined, and thus it is possible to reducethe memory bandwidth required for an external memory.

Furthermore, in the affine motion compensation prediction, the motionestimation range or the motion compensation range may be determined inaccordance with motion*estimation processing power depending oncomputational processing power on an encoder side or memory band width.With this, the limit on the range within which the motion estimation orthe motion compensation is performed can be determined in accordancewith the estimation processing power, and thus it is possible not onlyto reduce the amount of processing in accordance with the estimationprocessing power but also to efficiently perform motion compensationusing affine motion compensation.

Furthermore, in the affine motion compensation prediction, the limit onthe motion estimation range or the motion compensation range may includea limit on reference pictures in addition to a limit on a range ofreferable pixels. With this, it is possible not only to reduce thememory bandwidth required for an external memory but also to efficientlyperform motion compensation using affine motion compensation.

Furthermore, in the affine motion compensation prediction, informationabout the limit on the motion estimation range or the motioncompensation range may be included in header information of a videoparameter set (VPS), a sequence parameter set (SPS), or a pictureparameter set (PPS) of an encoded bitstream. With this, motioncompensation using affine motion compensation can be efficientlyperformed.

Furthermore, in the affine motion compensation prediction, theinformation about the limit on the motion estimation range or the motioncompensation range may include information for limiting referencepictures in addition to information for limiting a range of referablepixels. With this, it is possible not only to reduce the memorybandwidth required for an external memory but also to efficientlyperform motion compensation using affine motion compensation.

Furthermore, in the affine motion compensation prediction, theinformation about the limit on the motion estimation range or the motioncompensation range may include only information on whether a limit isplaced on motion estimation range and the motion compensation range.

Note that in the upper level system, when the information about thelimit on the motion estimation range or the motion compensation range ispredetermined or exchanged between a transmitter and a receiver, thisinformation need not be included in header information of the encodedbitstream such as VPS, SPS, PPS, etc.

Furthermore, in the limiting of the reference pictures, a total numberof reference pictures is specified, and the reference pictures may belimited to only the specified reference pictures selected in order ofincreasing reference index.

Variation 2

Note that in the limiting of the reference pictures, when temporalscalable encoding/decoding is performed, a total number of referencepictures is specified for reference pictures in a layer lower than orequal to that of a current picture to be encoded and/or decodedindicated by the time identifier, and the reference pictures may belimited to only the specified reference pictures selected in order ofincreasing reference index.

Furthermore, in the limiting of the reference pictures, a total numberof reference pictures is specified, and the reference pictures may belimited to only the specified reference pictures selected in order ofpicture order count (POC) indicating the order of output of picturesfrom a reference picture close to the current picture to be encoded.

Furthermore, in the limiting of the reference pictures, when temporalscalable encoding is performed, a total number of reference pictures isspecified for reference pictures in a layer lower than or equal to thatof a current picture to be encoded indicated by the time identifier, andthe reference pictures may be limited to only the specified referencepictures selected in order of picture order count (POC) indicating theorder of output of pictures from a reference picture close to thecurrent picture to be encoded/decoded.

[Implementation Example of Encoder]

FIG. 18 is a block diagram illustrating an implementation example ofencoder 100 according to Embodiment 1. Encoder 100 includes circuitry160 and memory 162. For example, the components in encoder 100 shown inFIGS. 1 and 13 are implemented as circuitry 160 and memory 162 shown inFIG. 18.

Circuitry 160 performs information processing, and is accessible tomemory 162. For example, circuitry 160 is a dedicated or general-purposeelectronic circuit, for encoding a video. Circuitry 160 may be aprocessor such as a CPU. Circuitry 160 also may be an assembly ofelectronic circuits. Furthermore, for example, circuitry 160 may serveas components other than components for storing information among thecomponents in encoder 100 shown in FIG. 1, etc.

Memory 162 is a dedicated or general-purpose memory that storesinformation for encoding a video in circuitry 160. Memory 162 may be anelectronic circuit, and be connected to circuitry 160. Memory 162 alsomay be included in circuitry 160. Memory 162 also may be an assembly ofelectronic circuits. Memory 162 also may be a magnetic disk, an opticaldisk, etc., and be referred to as a storage, a recording medium, etc.Memory 162 also may be a non-volatile memory or a volatile memory.

For example, memory 162 may store a video to be encoded, or a bitstreamcorresponding to the encoded video. Memory 162 also may store a programfor encoding a video in circuitry 160.

Furthermore, for example, memory 162 may serve as components for storinginformation among the components in encoder 100 shown in FIG. 1, etc. Inparticular, memory 162 may serve as block memory 118 and frame memory122 shown in FIG. 1. More specifically, memory 162 may store areconstructed block, a reconstructed picture, etc.

Note that in encoder 100, all the components shown in FIG. 1, etc., neednot be implemented, or all the foregoing processes need not beperformed. Some of the components shown in FIG. 1, etc., may be includedin another device, or some of the foregoing processes may be performedby another device. Then, in encoder 100, some of the components shown inFIG. 1, etc., are implemented and some of the forging processes areperformed, and thereby the motion compensation is effectively performed.

Hereinafter, an operation example of encoder 100 shown in FIG. 18 willbe described. In the following operation example, affine motioncompensation prediction is a process for deriving a motion vector foreach sub-block based on motion vectors of neighboring blocks in theinter prediction for a current block.

FIG. 19 is a flow chart for illustrating an operation example of encoder100 shown in FIG. 18. For example, in encoding a video using motioncompensation, encoder 100 shown in FIG. 18 performs the operation shownin FIG. 19.

In particular, using memory 162, circuitry 160 in encoder 100, in affinemotion compensation prediction in inter prediction for a current block,places a limit on a range within which motion estimation or motioncompensation is performed, and performs the motion compensation for thecurrent block (S311).

With this, encoder 100 can efficiently perform motion compensation usingaffine motion compensation. More specifically, a limit is placed on arange within which motion estimation or motion compensation is performedin affine motion compensation prediction, thereby allowing reduction inthe variation between control point motion vectors in affine motioncompensation prediction. Accordingly, the affine motion compensationprediction is more likely to be selected in the inter perdition, andthus the motion compensation can be efficiently performed using affinemotion compensation. It is also possible to place a limit on the regionof a reference picture to be obtained, thereby having the possibility ofreducing the memory bandwidth required for an external memory, i.e. aframe memory.

[Implementation Example of Decoder]

FIG. 20 is a block diagram illustrating an implementation example ofdecoder 200 according to embodiment 1. Decoder 200 includes circuitry260 and memory 262. For example, the components in decoder 200 shown inFIG. 10 are implemented as circuitry 260 and memory 262 shown in FIG.20.

Circuitry 260 performs information processing, and is accessible tomemory 262. For example, circuitry 260 is a dedicated or general-purposeelectronic circuit for decoding a video. Circuitry 260 may be aprocessor such as a CPU. Circuitry 260 also may be an assembly ofelectronic circuits. Furthermore, for example, circuitry 260 may serveas components other than components for storing information among thecomponents in decoder 200 shown in FIG. 10, etc.

Memory 262 is a dedicated or general-purpose memory that storesinformation for decoding a video in circuitry 260. Memory 262 may be anelectronic circuit, and be connected to circuitry 260. Memory 262 alsomay be included in circuitry 260. Memory 262 also may be an assembly ofelectronic circuits. Memory 262 also may be a magnetic disk, an opticaldisk, etc., and be referred to as a storage, a recording medium, etc.Memory 262 also may be a non-volatile memory or a volatile memory.

For example, memory 262 may store a bitstream corresponding to anencoded video, or a video corresponding to a decoded bitstream. Memory262 also may store a program for decoding a video in circuitry 260.

Furthermore, for example, memory 262 may serve as components for storinginformation among the components in decoder 200 shown in FIG. 10, etc.In particular, memory 262 may serve as block memory 210 and frame memory214 shown in FIG. 10. More specifically, memory 262 may store areconstructed block, a reconstructed picture, etc.

Note that in decoder 200, all the components shown in FIG. 10, etc.,need not be implemented, or all the foregoing processes need not beperformed. Some of the components shown in FIG. 10, etc., may beincluded in another device, or some of the foregoing processes may beperformed by another device. Then, in decoder 200, some of thecomponents shown in FIG. 10, etc, are implemented and some of theforging processes are performed, and thereby the motion compensation iseffectively performed.

Hereinafter, an operation example of decoder 200 shown in FIG. 20 willbe described. In the following operation example, affine motioncompensation prediction is a process for deriving a motion vector foreach subblock based on motion vectors of neighboring blocks in the interprediction for a current block.

FIG. 21 is a flow chart for illustrating operation example of decoder200 shown in FIG. 20. For example, in decoding a video using motioncompensation, decoder 200 shown in FIG. 20 performs the operation shownin FIG. 21.

In particular, using memory 262, circuitry 260 in decoder 200, in affinemotion compensation prediction in inter prediction for a current block,places a limit on a range within which motion estimation or motioncompensation is performed, and performs the motion compensation for thecurrent block (S411). Subsequently, the encoded stream is decoded(S412).

With this, decoder 200 can efficiently perform motion compensation usingaffine motion compensation. More specifically, a limit is placed on arange within which motion estimation or motion compensation is performedin affine motion compensation prediction, thereby allowing reduction inthe variation between control point motion vectors in affine motioncompensation prediction. Accordingly, the affine motion compensationprediction is more likely to be selected in the inter perdition, andthus the motion compensation can be efficiently performed using affinemotion compensation. It is also possible to place a limit on the regionof a reference picture to be obtained, thereby having the possibility ofreducing the memory bandwidth required for an external memory; i.e. aframe memory.

[Supplementary]

Furthermore, encoder 100 and decoder 200 according to the presentembodiment may be used as an image encoder and an image decoder, or maybe used as a video encoder or a video decoder, respectively.Alternatively, encoder 100 and decoder 200 are applicable as an interprediction device (an inter-picture prediction device).

In other words, encoder 100 and decoder 200 may correspond to only interpredictor (inter-picture predictor) 126 and inter predictor(inter-picture predictor) 218, respectively. The remaining componentssuch as transformer 106, inverse transformer 206, etc., may be includedin another device.

Furthermore, in the present embodiment, each component may be configuredby a dedicated hardware, or may be implemented by executing a softwareprogram suitable for each component. Each component may be implementedby causing a program executer such as a CPU or a processor to read outand execute a software program stored on a recording medium such as ahard disk or a semiconductor memory.

In particular, encoder 100 and decoder 200 may each include processingcircuitry and a storage which is electrically connected to theprocessing circuitry and is accessible from the processing circuitry.For example, the processing circuitry corresponds to circuitry 160 or260, and the storage corresponds to memory 162 or 262.

The processing circuitry includes at least one of a dedicated hardwareand a program executer, and performs processing using the storage.Furthermore, when the processing circuitry includes the programexecuter, the storage stores a software program to be executed by theprogram executer.

Here, a software for implementing encoder 100, decoder 200, etc.,according to the present embodiment is a program as follows.

In other words, the program may cause a computer to execute an encodingmethod including, in affine motion compensation prediction in interprediction for a current block, placing a limit on a range within whichmotion estimation or motion compensation is performed, and performingthe motion compensation for the current block.

Alternatively, the program may cause a computer to execute a decodingmethod including, in affine motion compensation prediction in interprediction for a current block, placing a limit, on a range within whichmotion estimation or motion compensation is performed, and performingthe motion compensation for the current block to decode an encodedstream.

Furthermore, as described above, each component may be a circuit. Thecircuits may be integrated into a single circuit as a whole, or may beseparated from each other. Furthermore, each component may beimplemented as a general-purpose processor, or as a dedicated processor.

Furthermore, a process performed by a specific component may beperformed by another component. Furthermore, the order of processes maybe changed, or multiple processes may be performed in parallel.Furthermore, an encoding and decoding device may include encoder 100 anddecoder 200.

The ordinal numbers used in the illustration such as first and secondmay be renumbered as needed. Furthermore, the ordinal number may benewly assigned to a component, etc., or may be deleted from a component,etc.

As described above, the aspects of encoder 100 and decoder 200 have beendescribed based on the embodiment, but the aspects of encoder 100 anddecoder 200 are not limited to this embodiment. Various modifications tothe embodiment that can be conceived by those skilled in the art, andforms configured by combining components in different embodimentswithout departing from the spirit of the present invention may beincluded in the scope of the aspects of encoder 100 and decoder 200.

This aspect may be implemented in combination with one or more of theother aspects according to the present disclosure. In addition, part ofthe processes in the flowcharts, part of the constituent elements of theapparatuses, and part, of the syntax described in this aspect may beimplemented in combination with other aspects.

Embodiment 2

As described in each of the above embodiment, each functional block cantypically be realized as an MPU and memory, for example. Moreover,processes performed by each of the functional blocks are typicallyrealized by a program execution unit, such as a processor, reading andexecuting software (a program) recorded on a recording medium such asROM. The software may be distributed via, for example, downloading, andmay be recorded on a recording medium such as semiconductor memory anddistributed. Note that each functional block can, of course, also berealized as hardware (dedicated circuit).

Moreover, the processing described in each of the embodiments may berealized via integrated processing using a single apparatus (system),and, alternatively, may be realized via decentralized processing using aplurality of apparatuses. Moreover, the processor that executes theabove-described program may be a single processor or a plurality ofprocessors. In other words, integrated processing may be performed, and,alternatively, decentralized processing may be performed.

Embodiments of the present disclosure are not limited to the aboveexemplary embodiments; various modifications may be made to theexemplary embodiments, the results of which are also included within thescope of the embodiments of the present disclosure.

Next, application examples of the moving picture encoding method (imageencoding method) and the moving picture decoding method (image decodingmethod) described in each of the above embodiments and a system thatemploys the same will be described. The system is characterized asincluding an image encoder that employs the image encoding method, animage decoder that employs the image decoding method, and an imageencoder/decoder that includes both the image encoder and the imagedecoder. Other configurations included in the system may be modified ona case-by-case basis.

Usage Examples

FIG. 22 illustrates an overall configuration of content providing systemex100 for implementing a content distribution service. The area in whichthe communication service is provided is divided into cells of desiredsizes, and base stations ex106, ex107, ex108, ex109, and ex110, whichare fixed wireless stations, are located in respective cells.

In content providing system ex100, devices including computer ex111,gaming device ex112, camera ex113, home appliance ex114, and smartphoneex110 are connected to internet ex101 via internet service providerex102 or communications network ex104 and base stations ex106 throughex110. Content providing system ex100 may combine and connect anycombination of the above elements. The devices may be directly orindirectly connected together via a telephone network or near fieldcommunication rather than via base stations ex106 through ex110, whichare fixed wireless stations. Moreover, streaming server ex103 isconnected to devices including computer ex111, gaming device ex112,camera ex113, home appliance ex114, and smartphone ex115 via, forexample, internet ex101. Streaming server ex103 is also connected to,for example, a terminal in a hotspot in airplane ex117 via satelliteex116.

Note that instead of base stations ex106 through ex110, wireless accesspoints or hotspots may be used. Streaming server ex103 may be connectedto communications network ex104 directly instead of via internet ex101or internet service provider ex102, and may be connected to airplaneex117 directly instead of via satellite ex116.

Camera ex113 is a device capable of capturing still images and video,such as a digital camera. Smartphone ex115 is a smartphone device,cellular phone, or personal handyphone system (PUS) phone that canoperate under the mobile communications system standards of the typical2G, 3G, 3.9G, and 4G systems, as well as the next-generation 5G system.

Home appliance ex118 is, for example, a refrigerator or a deviceincluded in a home fuel cell cogeneration system.

In content providing system ex100, a terminal including an image and/orvideo capturing function is capable of, for example, live streaming byconnecting to streaming server ex103 via, for example, base stationex106. When live streaming, a terminal (e.g., computer ex111, gamingdevice ex112, camera ex113, home appliance ex114, smartphone ex115, orairplane ex117) performs the encoding processing described in the aboveembodiments on still-image or video content captured by a user via theterminal, multiplexes video data obtained via the encoding and audiodata obtained by encoding audio corresponding to the video, andtransmits the obtained data to streaming server ex103. In other words,the terminal functions as the image encoder according to one aspect ofthe present disclosure.

Streaming server ex105 streams transmitted content data to clients thatrequest the stream. Client examples include computer ex111, gamingdevice ex112, camera ex113, home appliance ex114, smartphone ex115, andterminals inside airplane ex117, which are capable of decoding theabove-described encoded data. Devices that receive the streamed datadecode and reproduce the received data. In other words, the devices eachfunction as the image decoder according to one aspect of the presentdisclosure.

[Decentralized Processing]

Streaming server ex103 may be realized as a plurality of servers orcomputers between which tasks such as the processing, recording, andstreaming of data are divided. For example, streaming server ex103 maybe realized as a content delivery network (CDN) that streams content viaa network connecting multiple edge servers located throughout the world.In a CDN, an edge server physically near the client, is dynamicallyassigned to the client. Content is cached and streamed to the edgeserver to reduce load times. In the event of, for example, some kind ofan error or a change in connectivity due to, for example, a spike intraffic, it is possible to stream data stably at high speeds since it ispossible to avoid affected parts of the network by, for example,dividing the processing between a plurality of edge servers or switchingthe streaming duties to a different edge server, and continuingstreaming.

Decentralization is not limited to just the division of processing forstreaming; the encoding of the captured data may be divided between andperformed by the terminals, on the server side, or both. In one example,in typical encoding, the processing is performed in two loops. The firstloop is for detecting how complicated the image is on a frame-by-frameor scene by-scene basis, or detecting the encoding load. The second loopis for processing that maintains image quality and improves encodingefficiency. For example, it is possible to reduce the processing load ofthe terminals and improve the quality and encoding efficiency of thecontent by having the terminals perform the first loop of the encodingand having the server side that received the content perform the secondloop of the encoding. In such a case, upon receipt of a decodingrequest, it is possible for the encoded data resulting from the firstloop performed by one terminal to be received and reproduced on anotherterminal in approximately real time. This makes it possible to realizesmooth, real time streaming.

In another example, camera ex113 or the like extracts a feature amountfrom an image, compresses data related to the feature amount asmetadata, and transmits the compressed metadata to a server. Forexample, the server determines the significance of an object based onthe feature amount and changes the quantization accuracy accordingly toperform compression suitable for the meaning of the image. Featureamount data is particularly effective in improving the precision andefficiency of motion vector prediction during the second compressionpass performed by the server. Moreover, encoding that has a relativelylow processing load, such as variable length coding (VLC), may behandled by the terminal, and encoding that has a relatively highprocessing load, such as context-adaptive binary arithmetic coding(CABAC), may be handled by the server.

In yet another example, there are instances in which a plurality ofvideos of approximately the same scene are captured by a plurality ofterminals in, for example, a stadium, shopping mail, or factory. In sucha case, for example, the encoding may be decentralized by dividingprocessing tasks between the plurality of terminals that captured thevideos and, if necessary, other terminals that did not capture thevideos and the server, on a per unit basis. The units may be, forexample, groups of pictures (GOP), pictures, or tiles resulting fromdividing a picture. This makes it possible to reduce load times andachieve streaming that is closer to real time.

Moreover, since the videos are of approximately the same scene,management and/or instruction may be carried out by the server so that,the videos captured by the terminals can be cross-referenced. Moreover,the server may receive encoded data from the terminals, change referencerelationship between items of data or correct or replace picturesthemselves, and then perform the encoding. This makes it possible togenerate a stream with increased quality and efficiency for theindividual items of data.

Moreover, the server may stream video data after performing transcodingto convert the encoding format of the video data. For example, theserver may convert the encoding format from MPEG to VP, and may convertH.264 to H.265.

In this way, encoding can be performed by a terminal or one or moreservers. Accordingly, although the device that performs the encoding isreferred to as a “server” or “terminal” in the following description,some or all of the processes performed by the server may be performed bythe terminal, and likewise some or all of the processes performed by theterminal may be performed by the server. This also applies to decodingprocesses.

[3D, Multi-Angle]

In recent years, usage of images or videos combined from images orvideos of different scenes concurrently captured or the same scenecaptured from different angles by a plurality of terminals such ascamera ex113 and/or smartphone ex115 has increased. Videos captured bythe terminals are combined based on, for example, theseparately-obtained relative positional relationship between theterminals, or regions in a video having matching feature points.

In addition to the encoding of two-dimensional moving pictures, theserver may encode a still image based on scene analysis of a movingpicture either automatically or at a point in time specified by theuser, and transmit the encoded still image to a reception terminal.Furthermore, when the server can obtain the relative positionalrelationship between the video capturing terminals, in addition totwo-dimensional moving pictures, the server can generatethree-dimensional geometry of a scene based on video of the same scenecaptured from different angles. Note that the server may separatelyencode three-dimensional data generated from, for example, a pointcloud, and may, based on a result of recognizing or tracking a person orobject using three-dimensional data, select or reconstruct and generatea video to be transmitted to a reception terminal from videos capturedby a plurality of terminals.

This allows the user to enjoy a scene by freely selecting videoscorresponding to the video capturing terminals, and allows the user toenjoy the content obtained by extracting, from three-dimensional datareconstructed from a plurality of images or videos, a video from aselected viewpoint. Furthermore, similar to with video, sound may berecorded from relatively different angles, and the server may multiplex,with the video, audio from a specific angle or space in accordance withthe video, and transmit the result.

In recent years, content that is a composite of the real world and avirtual world, such as virtual reality (VR) and augmented reality (AR)content, has also become popular. In the case of VR images, the servermay create images from the viewpoints of both the left and right eyesand perform encoding that tolerates reference between the two viewpointimages, such as multi-view coding (MVC), and, alternatively, may encodethe images as separate streams without referencing. When the images aredecoded as separate streams, the streams may be synchronized whenreproduced so as to recreate a virtual three-dimensional space inaccordance with the viewpoint of the user.

In the case of AR images, the server superimposes virtual objectinformation existing in a virtual space onto camera informationrepresenting a real-world space, based on a three-dimensional positionor movement from the perspective of the user. The decoder may obtain orstore virtual object information and three-dimensional data, generatetwo-dimensional images based on movement from the perspective of theuser, and then generate superimposed data by seamlessly connecting theimages. Alternatively, the decoder may transmit, to the server, motionfrom the perspective of the user in addition to a request for virtualobject information, and the server may generate superimposed data basedon three-dimensional data stored in the server in accordance with thereceived motion, and encode and stream the generated superimposed datato the decoder. Note that superimposed data includes, in addition to RGBvalues, an a value indicating transparency, and the server sets the αvalue for sections other than the object generated fromthree-dimensional data to, for example, 0, and may perform the encodingwhile those sections are transparent. Alternatively, the server may setthe background to a predetermined RGB value, such as a chroma key, andgenerate data in which areas other than the object are set as thebackground.

Decoding of similarly streamed data may be performed by the client(i.e., the terminals), on the server side, or divided therebetween. Inone example, one terminal may transmit a reception request to a server,the requested content may be received and decoded by another terminal,and a decoded signal may be transmitted to a device having a display. Itis possible to reproduce high image quality data by decentralizingprocessing and appropriately selecting content regardless of theprocessing ability of the communications terminal itself. In yet anotherexample, while a TV, for example, is receiving image data that is largein size, a region of a picture, such as a tile obtained by dividing thepicture, may be decoded and displayed on a personal terminal orterminals of a viewer or viewers of the TV. This makes it possible forthe viewers to share a big*picture view as well as for each viewer tocheck his or her assigned area or inspect a region in further detail upclose.

In the future, both indoors and outdoors, in situations in which aplurality of wireless connections are possible over near, mid, and fardistances, it is expected to be able to seamlessly receive content evenwhen switching to data appropriate for the current connection, using astreaming system standard such as MPEG-DASH. With this, the user canswitch between data in real time while freely selecting a decoder ordisplay apparatus including not only his or her own terminal, but also,for example, displays disposed indoors or outdoors. Moreover, based on,for example, information on the position of the user, decoding can beperformed while switching which terminal handles decoding and whichterminal handles the displaying of content. This makes it possible to,while in route to a destination, display, on the wall of a nearbybuilding in which a device capable of displaying content is embedded oron part of the ground, map information while on the move. Moreover, itis also possible to switch the bit rate of the received data based onthe accessibility to the encoded data on a network, such as when encodeddata is cached on a server quickly accessible from the receptionterminal or when encoded data is copied to an edge server in a contentdelivery service.

[Scalable Encoding]

The switching of content will be described with reference to a scalablestream, illustrated in FIG. 23, that is compression coded viaimplementation of the moving picture encoding method described in theabove embodiments. The server may have a configuration in which contentis switched while making use of the temporal and/or spatial scalabilityof a stream, which is achieved by division into and encoding of layers,as illustrated in FIG. 23. Note that there may be a plurality ofindividual streams that are of the same content but different quality.In other words, by determining which layer to decode up to based oninternal factors, such as the processing ability on the decoder side,and external factors, such as communication bandwidth, the decoder sidecan freely switch between low resolution content and high resolutioncontent while decoding. For example, in a case in which the user wantsto continue watching, at home on a device such as a TV connected to theinternet, a video that he or she had been previously watching onsmartphone ex110 while on the move, the device can simply decode thesame stream up to a different layer, which reduces server side load.

Furthermore, in addition to the configuration described above in whichscalability is achieved as a result of the pictures being encoded perlayer and the enhancement layer is above the base layer, the enhancementlayer may include metadata based on, for example, statisticalinformation on the image, and the decoder side may generate high imagequality content by performing super resolution imaging on a picture inthe base layer based on the metadata. Super-resolution imaging may beimproving the SN ratio while maintaining resolution and/or increasingresolution. Metadata includes information for identifying a linear or anon-linear filter coefficient used in super resolution processing, orinformation identifying a parameter value in filter processing, machinelearning, or least squares method used in super-resolution processing.

Alternatively, a configuration in which a picture is divided into, forexample, tiles in accordance with the meaning of, for example, an objectin the image, and on the decoder side, only a partial region is decodedby selecting a tile to decode, is also acceptable. Moreover, by storingan attribute about the object (person, car, ball, etc.) and a positionof the object in the video (coordinates in identical images) asmetadata, the decoder side can identify the position of a desired objectbased on the metadata and determine which tile or tiles include thatobject. For example, as illustrated in FIG. 24, metadata is stored usinga data storage structure different from pixel data such as an SEImessage in HEVC. This metadata indicates, for example, the position,size, or color of the main object.

Moreover, metadata may be stored in units of a plurality of pictures,such as stream, sequence, or random access units. With this, the decoderside can obtain, for example, the time at which a specific personappears in the video, and by fitting that with picture unit information,can identify a picture in which the object is present and the positionof the object in the picture.

[Web Page Optimization]

FIG. 25 illustrates an example of a display screen of a web page on, forexample, computer ex111. FIG. 26 illustrates an example of a displayscreen of a web page on, for example, smartphone ex115. As illustratedin FIG. 25 and FIG. 26, a web page may include a plurality of imagelinks which are links to image content, and the appearance of the webpage differs depending on the device used to view the web page. When aplurality of image links are viewable on the screen, until the userexplicitly selects an image link, or until the image link is in theapproximate center of the screen or the entire image link fits in thescreen, the display apparatus (decoder) displays, as the image links,still images included in the content or I pictures, displays video suchas an animated gif using a plurality of still images or I pictures, forexample, or receives only the base layer and decodes and displays thevideo.

When an image link is selected by the user, the display apparatusdecodes giving the highest priority to the base layer. Note that ifthere is information in the HTML code of the web page indicating thatthe content is scalable, the display apparatus may decode up to theenhancement layer. Moreover, in order to guarantee real timereproduction, before a selection is made or when the bandwidth isseverely limited, the display apparatus can reduce delay between thepoint in time at which the leading picture is decoded and the point intime at which the decoded picture is displayed (that is, the delaybetween the start, of the decoding of the content, to the displaying ofthe content) by decoding and displaying only forward reference pictures(I picture, P picture, forward reference B picture). Moreover, thedisplay apparatus may purposely ignore the reference relationshipbetween pictures and coarsely decode all B and P pictures as forwardreference pictures, and then perform normal decoding as the number ofpictures received over time increases.

[Autonomous Driving]

When transmitting and receiving still image or video data such two- orthree-dimensional map information for autonomous driving or assisteddriving of an automobile, the reception terminal may receive, inaddition to image data belonging to one or more layers, information on,for example, the weather or road construction as metadata, and associatethe metadata with the image data upon decoding. Note that metadata maybe assigned per layer and, alternatively, may simply be multiplexed withthe image data.

In such a case, since the automobile, drone, airplane, etc., includingthe reception terminal is mobile, the reception terminal can seamlesslyreceive and decode while switching between base stations among basestations ex106 through ex110 by transmitting information indicating theposition of the reception terminal upon reception request. Moreover, inaccordance with the selection made by the user, the situation of theuser, or the bandwidth of the connection, the reception terminal candynamically select to what extent the metadata is received or to whatextent the map information, for example, is updated.

With this, in content providing system ex100, the client can receive,decode, and reproduce, in real time, encoded information transmitted bythe user.

[Streaming of Individual Content]

In content providing system ex100, in addition to high image quality,long content distributed by a video distribution entity, unicast, ormulticast streaming of low image quality, short content from anindividual is also possible. Moreover, such content from individuals islikely to further increase in popularity. The server may first performediting processing on the content before the encoding processing inorder to refine the individual content. This may be achieved with, forexample, the following configuration.

In real time while capturing video or image content or after the contenthas been captured and accumulated, the server performs recognitionprocessing based on the raw or encoded data, such as capture errorprocessing, scene search processing, meaning analysis, and/or objectdetection processing. Then, based on the result of the recognitionprocessing, the server—either when prompted or automatically—edits thecontent, examples of which include: correction such as focus and/ormotion blur correction; removing low-priority scenes such as scenes thatare low in brightness compared to other pictures or out of focus; objectedge adjustment; and color tone adjustment. The server encodes theedited data based on the result of the editing. It is known thatexcessively long videos tend to receive fewer views. Accordingly, inorder to keep the content within a specific length that scales with thelength of the original video, the server may, in addition to thelow-priority scenes described above, automatically clip out scenes withlow movement based on an image processing result. Alternatively, theserver may generate and encode a video digest based on a result of ananalysis of the meaning of a scene.

Note that there are instances in which individual content may includecontent that infringes a copyright, moral right, portrait rights, etc.Such an instance may lead to an unfavorable situation for the creator,such as when content is shared beyond the scope intended by the creator.Accordingly, before encoding, the server may, for example, edit imagesso as to blur faces of people in the periphery of the screen or blur theinside of a house, for example. Moreover, the server may be configuredto recognize the faces of people other than a registered person inimages to be encoded, and when such faces appear in an image, forexample, apply a mosaic filter to the face of the person. Alternatively,as pre- or post-processing for encoding, the user may specify, forcopyright reasons, a region of an image including a person or a regionof the background be processed, and the server may process the specifiedregion by, for example, replacing the region with a different image orblurring the region. If the region includes a person, the person may betracked in the moving picture, and the head region may be replaced withanother image as the person moves.

Moreover, since there is a demand for real-time viewing of contentproduced by individuals, which tends to be small in data size, thedecoder first receives the base layer as the highest priority andperforms decoding and reproduction, although this may differ dependingon bandwidth. When the content is reproduced two or more times, such aswhen the decoder receives the enhancement layer during decoding andreproduction of the base layer and loops the reproduction, the decodermay reproduce a high image quality video including the enhancementlayer. If the stream is encoded using such scalable encoding, the videomay be low quality when in an unselected state or at the start of thevideo, but it can offer an experience in which the image quality of thestream progressively increases in an intelligent manner. This is notlimited to just scalable encoding; the same experience can be offered byconfiguring a single stream from a low quality stream reproduced for thefirst time and a second stream encoded using the first stream as areference.

Other Usage Examples

The encoding and decoding may be performed by LSI ex500, which istypically included in each terminal. LSI ex500 may be configured of asingle chip or a plurality of chips. Software for encoding and decodingmoving pictures may be integrated into some type of a recording medium(such as a CD-ROM, a flexible disk, or a hard disk) that is readable by,for example, computer ex111, and the encoding and decoding may beperformed using the software. Furthermore, when smartphone ex115 isequipped with a camera, the video data obtained by the camera may betransmitted. In this case, the video data is coded by LSI ex500 includedin smartphone ex115.

Note that LSI ex500 may be configured to download and activate anapplication. In such a case, the terminal first determines whether it iscompatible with the scheme used to encode the content or whether it iscapable of executing a specific service. When the terminal is notcompatible with the encoding scheme of the content or when the terminalis not capable of executing a specific service, the terminal firstdownloads a codec or application software then obtains and reproducesthe content.

Aside from the example of content providing system ex100 that usesinternet ex101, at least the moving picture encoder (image encoder) orthe moving picture decoder (image decoder) described in the aboveembodiments may be implemented in a digital broadcasting system. Thesame encoding processing and decoding processing may be applied totransmit and receive broadcast radio waves superimposed with multiplexedaudio and video data using, for example, a satellite, even though thisis geared toward multicast whereas unicast is easier with contentproviding system ex100.

[Hardware Configuration]

FIG. 27 illustrates smartphone ex115. FIG. 28 illustrates aconfiguration example of smartphone ex115. Smartphone ex115 includesantenna ex450 for transmitting and receiving radio waves to and frombase station ex110, camera ex465 capable of capturing video and stillimages, and display ex458 that displays decoded data, such as videocaptured by camera ex465 and video received by antenna ex450. Smartphoneex115 further includes user interface ex466 such as a touch panel, audiooutput unit ex457 such as a speaker for outputting speech or otheraudio, audio input unit ex456 such as a microphone for audio input,memory ex467 capable of storing decoded data such as captured video orstill images, recorded audio, received video or still images, and mail,as well as decoded data, and slot ex464 which is an interface for SIMex468 for authorizing access to a network and various data. Note thatexternal memory may be used instead of memory ex467.

Moreover, main controller ex460 which comprehensively controls displayex458 and user interface ex466, power supply circuit ex461, userinterface input controller ex462, video signal processor ex455, camerainterface ex463, display controller ex459, modulator/demodulator ex452,multiplexer/demultiplexer ex453, audio signal processor ex454, slotex464, and memory ex467 are connected via bus ex470.

When the user turns the power button of power supply circuit ex461 on,smartphone ex115 is powered on into an operable state by each componentbeing supplied with power from a battery pack.

Smartphone ex115 performs processing for, for example, calling and datatransmission, based on control performed by main controller ex460, whichincludes a CPU, ROM, and RAM. When making calls, an audio signalrecorded by audio input unit ex456 is converted into a digital audiosignal by audio signal processor ex454, and this is applied with spreadspectrum processing by modulator/demodulator ex452 and digital-analogconversion and frequency conversion processing by transmitter/receiverex451, and then transmitted via antenna ex450. The received data isamplified, frequency converted, and analog-digital converted, inversespread spectrum processed by modulator/demodulator ex452, converted intoan analog audio signal by audio signal processor ex454, and then outputfrom audio output unit ex457. In data transmission mode, text,still-image, or video data is transmitted by main controller ex460 viauser interface input controller ex462 as a result of operation of, forexample, user interface ex466 of the main body, and similar transmissionand reception processing is performed. In data transmission mode, whensending a video, still image, or video and audio, video signal processorex455 compression encodes, via the moving picture encoding methoddescribed in the above embodiments, a video signal stored in memoryex467 or a video signal input from camera ex465, and transmits theencoded video data to multiplexer/demultiplexer ex453. Moreover, audiosignal processor ex454 encodes an audio signal recorded by audio input,unit ex456 while camera ex465 is capturing, for example, a video orstill image, and transmits the encoded audio data tomultiplexer/demultiplexer ex453. Multiplexer/demultiplexer ex453multiplexes the encoded video data and encoded audio data using apredetermined scheme, modulates and converts the data usingmodulator/demodulator (modulator/demodulator circuit) ex452 andtransmitter/receiver ex451, and transmits the result via antenna ex450.

When video appended in an email or a chat, or a video linked from a webpage, for example, is received, in order to decode the multiplexed datareceived via antenna ex450, multiplexer/demultiplexer ex453demultiplexes the multiplexed data to divide the multiplexed data into abitstream of video data and a bitstream of audio data, supplies theencoded video data to video signal processor ex455 via synchronous busex470, and supplies the encoded audio data to audio signal processorex454 via synchronous bus ex470. Video signal processor ex455 decodesthe video signal using a moving picture decoding method corresponding tothe moving picture encoding method described in the above embodiments,and video or a still image included in the linked moving picture file isdisplayed on display ex458 via display controller ex459. Moreover, audiosignal processor ex454 decodes the audio signal and outputs audio fromaudio output unit ex457. Note that since realtime streaming is becomingmore and more popular, there are instances in which reproduction of theaudio may be socially inappropriate depending on the user's environment.Accordingly, as an initial value, a configuration in which only videodata is reproduced, i.e., the audio signal is not reproduced, ispreferable. Audio may be synchronized and reproduced only when an input,such as when the user clicks video data, is received.

Although smartphone ex115 was used in the above example, threeimplementations are conceivable: a transceiver terminal including bothan encoder and a decoder; a transmitter terminal including only anencoder; and a receiver terminal including only a decoder. Further, inthe description of the digital broadcasting system, an example is givenin which multiplexed data obtained as a result of video data beingmultiplexed with, for example, audio data, is received or transmitted,but the multiplexed data may be video data multiplexed with data otherthan audio data, such as text data related to the video. Moreover, thevideo data itself rather than multiplexed data maybe received ortransmitted.

Although main controller ex460 including a CPU is described ascontrolling the encoding or decoding processes, terminals often includeGPUs. Accordingly, a configuration is acceptable in which a large areais processed at once by making use of the performance ability of the GPUvia memory shared by the CPU and GPU or memory including an address thatis managed so as to allow common usage by the CPU and GPU. This makes itpossible to shorten encoding time, maintain the real-time nature of thestream, and reduce delay. In particular, processing relating to motionestimation, deblocking filtering, sample adaptive offset (SAO), andtransformation/quantization can be effectively carried out by the GPUinstead of the CPU in units of, for example pictures, all at once.

Although only some exemplary embodiments of the present disclosure havebeen described in detail above, those skilled in the art will readilyappreciate that many modifications are possible in the exemplaryembodiments without materially departing from the novel teachings andadvantages of the present disclosure. Accordingly, all suchmodifications are intended to be included within the scope of thepresent disclosure.

INDUSTRIAL APPLICABILITY

The present invention is applicable to a television receiver, a digitalvideo recorder, a car navigation system, a mobile phone, a digitalcamera, a digital video camera, a teleconference system, an electronicmirror, etc.

What is claimed is:
 1. An encoder comprising: circuitry; and memory,wherein using the memory, the circuitry, in affine motion compensationprediction in inter prediction for a current block, places a limit on arange within which motion estimation or motion compensation isperformed, and performs the motion compensation for the current block,and the limit on the range within which the motion estimation or themotion compensation is performed is placed so that a variation between acontrol point motion vector at a top left corner and a control pointmotion vector at a top right corner of the current block in the affinemotion compensation prediction falls within a predetermined range. 2.The encoder according to claim 1, wherein in the affine motioncompensation prediction, the limit on the range within which the motionestimation or the motion compensation is performed is newly determinedfor each current picture, or an appropriate set is selected for eachcurrent picture from among a plurality of predetermined sets of motionestimation ranges or a plurality of predetermined sets of motioncompensation ranges.
 3. The encoder according to claim 1, wherein in theaffine motion compensation prediction, the limit on the range withinwhich the motion, estimation or the motion compensation is performed ischanged in accordance with a type of a reference picture.
 4. The encoderaccording to claim 1, wherein in the affine motion compensationprediction, the limit on the range within which the motion estimation orthe motion compensation is performed is determined for eachpredetermined profile and level.
 5. The encoder according to claim 1,wherein in the affine motion compensation prediction, the limit on therange within which the motion estimation or the motion compensation isperformed is determined in accordance with motion-estimation processingpower depending on computational processing power on an encoder side ormemory bandwidth.
 6. The encoder according to claim 1, wherein in theaffine motion compensation prediction, the limit on the range withinwhich the motion estimation or the motion compensation is performedincludes a limit on reference pictures in addition to a limit on a rangeof referable pixels.
 7. The encoder according to claim 1, wherein in theaffine motion compensation prediction, information about the limit onthe range within which the motion estimation or the motion compensationis performed is included in header information of a video parameter set(VPS), a sequence parameter set (SPS), or a picture parameter set (PPS)of an encoded bitstream.
 8. The encoder according to claim 1, wherein inthe affine motion compensation prediction, the information about thelimit on the range within which the motion estimation or the motioncompensation is performed includes information for limiting referencepictures in addition to information for limiting a range of referablepixels.
 9. The encoder according to claim 1, wherein in the affinemotion compensation prediction, in the motion estimation for affineinter mode, when a region referred to by a motion vector derived from acurrent control point motion vector to be evaluated is outside the rangewithin which the motion estimation is performed, the current controlpoint motion vector is eliminated from candidates on which the motionestimation is performed.
 10. The encoder according to claim 1, whereinin the affine motion compensation prediction, in affine inter mode, whena region referred to by a motion vector derived from a control pointmotion vector predictor obtained from surrounding encoded blocksneighboring the current block is outside the range within which themotion estimation is performed, encoding is prevented from beingperformed in the affine inter mode.
 11. The encoder according to claim1, wherein in the affine motion compensation prediction, in affine mergemode, when a region referred to by a motion vector derived from acontrol point motion vector obtained from surrounding encoded blocksneighboring the current block is outside the range within which themotion compensation is performed, encoding is prevented from beingperformed in the affine merge mode.
 12. A decoder comprising: circuitry;and memory, wherein using the memory, the circuitry, in affine motioncompensation prediction in inter prediction for a current block, placesa limit on a range within which motion estimation or motion compensationis performed, and performs the motion compensation for the current blockto decode an encoded stream, and the limit on the range within which themotion estimation or the motion compensation is performed is placed sothat a variation between a control point motion vector at a top leftcorner and a control point motion vector at a top right corner of thecurrent block in the affine motion compensation prediction falls withina predetermined range.
 13. The decoder according to claim 12, wherein inthe affine motion compensation prediction, the limit on the range withinwhich the motion estimation or the motion compensation is performed isnewly determined for each current picture, or an appropriate set isselected for each current picture from among a plurality ofpredetermined sets of motion estimation ranges or a plurality ofpredetermined sets of motion compensation ranges.
 14. The decoderaccording to claim 12, wherein in the affine motion compensationprediction, the limit on the range within which the motion estimation orthe motion compensation is performed is changed in accordance with atype of a reference picture.
 15. The decoder according to claim 12,wherein in the affine motion compensation prediction, the limit on therange within which the motion estimation or the motion compensation isperformed is determined for each predetermined profile and level. 16.The decoder according to claim 12, wherein in the affine motioncompensation prediction, the limit on the range within which the motionestimation or the motion compensation is performed is determined inaccordance with motion-estimation processing power depending oncomputational processing power on an encoder side or memory bandwidth.17. The decoder according to claim 12, wherein in the affine motioncompensation prediction, the limit on the range within which the motionestimation or the motion compensation is performed includes a limit onreference pictures in addition to a limit on a range of referablepixels.
 18. The decoder according to claim 12, wherein in the affinemotion compensation prediction, information about the limit on the rangewithin which the motion estimation or the motion compensation isperformed is included in header information of a video parameter set(VPS), a sequence parameter set (SPS), or a picture parameter set (PPS)of an encoded bitstream.
 19. The decoder according to claim 12, whereinin the affine motion compensation prediction, the information about thelimit on the range within which the motion estimation or the motioncompensation is performed includes information for limiting referencepictures in addition to information for limiting a range of referablepixels.
 20. The decoder according to claim 12, wherein in the affinemotion compensation prediction, in the motion estimation for affineinter mode, when a region referred to by a motion vector derived from acurrent control point motion vector to be evaluated is outside the rangewithin which the motion estimation is performed, the current controlpoint motion vector is eliminated from candidates on which the motionestimation is performed.
 21. The decoder according to claim 12, whereinin the affine motion compensation prediction, in affine inter mode, whena region referred to by a motion vector derived from a control pointmotion vector predictor obtained from surrounding decoded blocksneighboring the current block is outside the range within which themotion estimation is performed, encoding is prevented from beingperformed in the affine inter mode.
 22. The decoder according to claim12, wherein in the affine motion compensation prediction, in affinemerge mode, when a region referred to by a motion vector derived from acontrol point motion vector obtained from surrounding decoded blocksneighboring the current, block is outside the range within which themotion compensation is performed, encoding is prevented from beingperformed in the affine merge mode.
 23. An encoding method comprising:in affine motion compensation prediction in inter prediction for acurrent block, placing a limit on a range within which motion estimationor motion compensation is performed, and performing the motioncompensation for the current block, wherein the limit on the rangewithin which the motion estimation or the motion compensation isperformed is placed so that a variation between a control point motionvector at a top left corner and a control point motion vector at a topright corner of the current block in the affine motion compensationprediction falls within a predetermined range.
 24. A decoding methodcomprising: in affine motion compensation prediction in inter predictionfor a current block, placing a limit on a range within which motionestimation or motion compensation is performed, and performing themotion compensation for the current block to decode an encoded stream,wherein the limit on the range within which the motion estimation or themotion compensation is performed is placed so that a variation between acontrol point motion vector at a top left corner and a control pointmotion vector at a top right corner of the current block in the affinemotion compensation prediction falls within a predetermined range.